fix: https://root-forum.cern.ch/t/wrong-branch-type-detection/59236/25

src/uproot/writing/_cascadetree.py

@@ -348,10 +348,11 @@ def _branch_np(
         if letter is None:
             raise TypeError(f"cannot write NumPy dtype {branch_dtype} in TTree")
 
-        if branch_shape == ():
-            dims = ""
-        else:
-            dims = "".join("[" + str(x) + "]" for x in branch_shape)
+        dims = ""
+        if counter is not None:
+            dims = "[" + counter["fName"] + "]"
+        if len(branch_shape) > 0:
+            dims = dims + "".join("[" + str(x) + "]" for x in branch_shape)
 
         title = f"{branch_name}{dims}/{letter}"
 

tests/test_1207_fix_title_of_TBranch_with_counter.py

@@ -0,0 +1,21 @@
+# BSD 3-Clause License; see https://github.com/scikit-hep/uproot5/blob/main/LICENSE
+
+import os
+
+import awkward as ak
+
+import uproot
+
+
+def test(tmp_path):
+    filename = os.path.join(tmp_path, "file.root")
+
+    with uproot.recreate(filename) as file:
+        file["tree"] = {"branch": ak.Array([[1.1, 2.2, 3.3], [], [4.4, 5.5]])}
+
+    with uproot.open(filename) as file:
+        assert file["tree"]["branch"].title == "branch[nbranch]/D"
+        assert (
+            file["tree"]["branch"].member("fLeaves")[0].member("fTitle")
+            == "branch[nbranch]"
+        )