diff --git a/cache-tree.c b/cache-tree.c
index d4f5af50545272..f7a679a973c9cc 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -449,6 +449,7 @@ static int update_one(struct cache_tree *it,
 
 int cache_tree_update(struct index_state *istate, int flags)
 {
+	uint64_t start = getnanotime();
 	struct cache_tree *it = istate->cache_tree;
 	struct cache_entry **cache = istate->cache;
 	int entries = istate->cache_nr;
@@ -460,6 +461,7 @@ int cache_tree_update(struct index_state *istate, int flags)
 	if (i < 0)
 		return i;
 	istate->cache_changed |= CACHE_TREE_CHANGED;
+	trace_performance_since(start, "repair cache-tree");
 	return 0;
 }
 
diff --git a/cache.h b/cache.h
index 9ea0c25a5d1c49..e73d3dc2a36e4c 100644
--- a/cache.h
+++ b/cache.h
@@ -670,6 +670,7 @@ extern int index_name_pos(const struct index_state *, const char *name, int name
 #define ADD_CACHE_JUST_APPEND 8		/* Append only; tree.c::read_tree() */
 #define ADD_CACHE_NEW_ONLY 16		/* Do not replace existing ones */
 #define ADD_CACHE_KEEP_CACHE_TREE 32	/* Do not invalidate cache-tree */
+#define ADD_CACHE_SKIP_VERIFY_PATH 64	/* Do not verify path */
 extern int add_index_entry(struct index_state *, struct cache_entry *ce, int option);
 extern void rename_index_entry_at(struct index_state *, int pos, const char *new_name);
 
diff --git a/read-cache.c b/read-cache.c
index b79cd96a52b4bf..564e2bf75ad97a 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1237,6 +1237,7 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 	int ok_to_add = option & ADD_CACHE_OK_TO_ADD;
 	int ok_to_replace = option & ADD_CACHE_OK_TO_REPLACE;
 	int skip_df_check = option & ADD_CACHE_SKIP_DFCHECK;
+	int skip_verify_path = option & ADD_CACHE_SKIP_VERIFY_PATH;
 	int new_only = option & ADD_CACHE_NEW_ONLY;
 
 	if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
@@ -1277,7 +1278,7 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 
 	if (!ok_to_add)
 		return -1;
-	if (!verify_path(ce->name, ce->ce_mode))
+	if (!skip_verify_path && !verify_path(ce->name, ce->ce_mode))
 		return error("Invalid path '%s'", ce->name);
 
 	if (!skip_df_check &&
diff --git a/unpack-trees.c b/unpack-trees.c
index 802bff0a48050d..31727669d5ecc4 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -191,6 +191,7 @@ static int do_add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
 
 	ce->ce_flags = (ce->ce_flags & ~clear) | set;
 	return add_index_entry(&o->result, ce,
+			       o->extra_add_index_flags |
 			       ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 }
 
@@ -342,6 +343,7 @@ static int check_updates(struct unpack_trees_options *o)
 	struct progress *progress = NULL;
 	struct index_state *index = &o->result;
 	struct checkout state = CHECKOUT_INIT;
+	uint64_t start = getnanotime();
 	int i;
 
 	state.force = 1;
@@ -413,6 +415,7 @@ static int check_updates(struct unpack_trees_options *o)
 	errs |= finish_delayed_checkout(&state);
 	if (o->update)
 		git_attr_set_direction(GIT_ATTR_CHECKIN, NULL);
+	trace_performance_since(start, "update worktree after a merge");
 	return errs != 0;
 }
 
@@ -634,6 +637,132 @@ static inline int are_same_oid(struct name_entry *name_j, struct name_entry *nam
 	return name_j->oid && name_k->oid && !oidcmp(name_j->oid, name_k->oid);
 }
 
+static int all_trees_same_as_cache_tree(int n, unsigned long dirmask,
+					struct name_entry *names,
+					struct traverse_info *info)
+{
+	struct unpack_trees_options *o = info->data;
+	int i;
+
+	if (!o->merge || dirmask != ((1 << n) - 1))
+		return 0;
+
+	for (i = 1; i < n; i++)
+		if (!are_same_oid(names, names + i))
+			return 0;
+
+	return cache_tree_matches_traversal(o->src_index->cache_tree, names, info);
+}
+
+static int index_pos_by_traverse_info(struct name_entry *names,
+				      struct traverse_info *info)
+{
+	struct unpack_trees_options *o = info->data;
+	int len = traverse_path_len(info, names);
+	char *name = xmalloc(len + 1 /* slash */ + 1 /* NUL */);
+	int pos;
+
+	make_traverse_path(name, info, names);
+	name[len++] = '/';
+	name[len] = '\0';
+	pos = index_name_pos(o->src_index, name, len);
+	if (pos >= 0)
+		BUG("This is a directory and should not exist in index");
+	pos = -pos - 1;
+	if (!starts_with(o->src_index->cache[pos]->name, name) ||
+	    (pos > 0 && starts_with(o->src_index->cache[pos-1]->name, name)))
+		BUG("pos must point at the first entry in this directory");
+	free(name);
+	return pos;
+}
+
+/*
+ * Fast path if we detect that all trees are the same as cache-tree at this
+ * path. We'll walk these trees recursively using cache-tree/index instead of
+ * ODB since already know what these trees contain.
+ */
+static int traverse_by_cache_tree(int pos, int nr_entries, int nr_names,
+				  struct name_entry *names,
+				  struct traverse_info *info)
+{
+	struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
+	struct unpack_trees_options *o = info->data;
+	struct cache_entry *tree_ce = NULL;
+	int ce_len = 0;
+	int i, d;
+
+	if (!o->merge)
+		BUG("We need cache-tree to do this optimization");
+
+	/*
+	 * Try to keep add_index_entry() as fast as possible since
+	 * we're going to do a lot of them.
+	 *
+	 * Skipping verify_path() should totally be safe because these
+	 * paths are from the source index, which must have been
+	 * verified.
+	 *
+	 * Skipping D/F and cache-tree validation checks is trickier
+	 * because it assumes what n-merge code would do when all
+	 * trees and the index are the same. We probably could just
+	 * optimize those code instead (e.g. we don't invalidate that
+	 * many cache-tree, but the searching for them is very
+	 * expensive).
+	 */
+	o->extra_add_index_flags = ADD_CACHE_SKIP_DFCHECK;
+	o->extra_add_index_flags |= ADD_CACHE_SKIP_VERIFY_PATH;
+
+	/*
+	 * Do what unpack_callback() and unpack_nondirectories() normally
+	 * do. But we walk all paths recursively in just one loop instead.
+	 *
+	 * D/F conflicts and staged entries are not a concern because
+	 * cache-tree would be invalidated and we would never get here
+	 * in the first place.
+	 */
+	for (i = 0; i < nr_entries; i++) {
+		int new_ce_len, len, rc;
+
+		src[0] = o->src_index->cache[pos + i];
+
+		len = ce_namelen(src[0]);
+		new_ce_len = cache_entry_size(len);
+
+		if (new_ce_len > ce_len) {
+			new_ce_len <<= 1;
+			tree_ce = xrealloc(tree_ce, new_ce_len);
+			memset(tree_ce, 0, new_ce_len);
+			ce_len = new_ce_len;
+
+			tree_ce->ce_flags = create_ce_flags(0);
+
+			for (d = 1; d <= nr_names; d++)
+				src[d] = tree_ce;
+		}
+
+		tree_ce->ce_mode = src[0]->ce_mode;
+		tree_ce->ce_namelen = len;
+		oidcpy(&tree_ce->oid, &src[0]->oid);
+		memcpy(tree_ce->name, src[0]->name, len + 1);
+
+		rc = call_unpack_fn((const struct cache_entry * const *)src, o);
+		if (rc < 0) {
+			free(tree_ce);
+			return rc;
+		}
+
+		mark_ce_used(src[0], o);
+	}
+	o->extra_add_index_flags = 0;
+	free(tree_ce);
+	if (o->debug_unpack)
+		printf("Unpacked %d entries from %s to %s using cache-tree\n",
+		       nr_entries,
+		       o->src_index->cache[pos]->name,
+		       o->src_index->cache[pos + nr_entries - 1]->name);
+	return 0;
+}
+
 static int traverse_trees_recursive(int n, unsigned long dirmask,
 				    unsigned long df_conflicts,
 				    struct name_entry *names,
@@ -645,6 +774,17 @@ static int traverse_trees_recursive(int n, unsigned long dirmask,
 	void *buf[MAX_UNPACK_TREES];
 	struct traverse_info newinfo;
 	struct name_entry *p;
+	int nr_entries;
+
+	nr_entries = all_trees_same_as_cache_tree(n, dirmask, names, info);
+	if (nr_entries > 0) {
+		struct unpack_trees_options *o = info->data;
+		int pos = index_pos_by_traverse_info(names, info);
+
+		if (!o->merge || df_conflicts)
+			BUG("Wrong condition to get here buddy");
+		return traverse_by_cache_tree(pos, nr_entries, n, names, info);
+	}
 
 	p = names;
 	while (!p->mode)
@@ -811,6 +951,11 @@ static struct cache_entry *create_ce_entry(const struct traverse_info *info,
 	return ce;
 }
 
+/*
+ * Note that traverse_by_cache_tree() duplicates some logic in this function
+ * without actually calling it. If you change the logic here you may need to
+ * check and change there as well.
+ */
 static int unpack_nondirectories(int n, unsigned long mask,
 				 unsigned long dirmask,
 				 struct cache_entry **src,
@@ -995,6 +1140,11 @@ static void debug_unpack_callback(int n,
 		debug_name_entry(i, names + i);
 }
 
+/*
+ * Note that traverse_by_cache_tree() duplicates some logic in this funciton
+ * without actually calling it. If you change the logic here you may need to
+ * check and change there as well.
+ */
 static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *names, struct traverse_info *info)
 {
 	struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
@@ -1282,6 +1432,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	int i, ret;
 	static struct cache_entry *dfc;
 	struct exclude_list el;
+	uint64_t start = getnanotime();
 
 	if (len > MAX_UNPACK_TREES)
 		die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
@@ -1423,6 +1574,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 			goto done;
 		}
 	}
+	trace_performance_since(start, "unpack trees");
 
 	o->src_index = NULL;
 	ret = check_updates(o) ? (-2) : 0;
diff --git a/unpack-trees.h b/unpack-trees.h
index 6c48117b845fbf..5d719cacbe42e9 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -73,6 +73,7 @@ struct unpack_trees_options {
 	struct index_state result;
 
 	struct exclude_list *el; /* for internal use */
+	unsigned int extra_add_index_flags;
 };
 
 extern int unpack_trees(unsigned n, struct tree_desc *t,