Tree structures is a package for your project, with a handy implementation of trees for GameMaker Studio 2 using constructors. The package was originally written for the personal work of TornadoTech projects, but was uploaded to GitHub for the convenience of all developers.

Also, the root can have a value, but you can simply not declare a value, then it will default to undefined. To create a tree just write:

var tree = new Tree();
show_debug_message(tree.value); // undefined 

var tree2 = new Tree("Same data");
show_debug_message(tree2.value); // "Same data" 

You can add nodes to the root of the tree as well as to other nodes. To add a node, write,
add(key, value) and to turn it into a string you need to call the to_string() method

tree = new Tree();

// Layer 1
var node_a = tree.add("node_a", 10);
var node_b = tree.add("node_b", 7);

// Layer 2
var node_a2 = node_a.add("node_a2", 3);
var node_a3 = node_a.add("node_a3", 3);
var node_a4 = node_a.add("node_a4", 3);

// Layer 3
var node_c = node_a2.add("node_c", 20);
var node_d = node_a4.add("node_d", 37);

show_debug_message(tree.to_string());

// Result:
// [root]: undefined
// _ [node_a]: 10
// _ _ [node_a2]: 3
// _ _ _ [node_c]: 20
// _ _ [node_a3]: 3
// _ _ [node_a4]: 3
// _ _ _ [node_d]: 37
// _ [node_b]: 7

You can use exists(key) to check if a node exists, and remove(key) to remove it.

tree = new Tree();
// Layer 1
var node_a = tree.add("node_a", 23);
var node_b = tree.add("node_b", 29);

// Layer 2
var node_c = node_a.add("node_c", 48);

tree.exists("node_a"); // true
tree.exists("node_c"); // true
tree.exists("node_j"); // false

tree.remove("node_a");

tree.exists("node_a"); // false
tree.exists("node_c"); // false

And the main thing is of course you can get the find(key) node, which will return the tree structure. And to read and write information, you can refer to the key and value fields. And to get the parent, refer to parent.

tree = new Tree();

// Layer 1
var node_a = tree.add("node_a", 10);
var node_b = tree.add("node_b", 7);

// Layer 2
var node_a2 = node_a.add("node_a2", 3);
var node_a3 = node_a.add("node_a3", 3);
var node_a4 = node_a.add("node_a4", 3);

// Layer 3
var node_c = node_a2.add("node_c", 20);
var node_d = node_a4.add("node_d", 37);

var node = tree.find("node_d");
show_debug_message(node.value); // 37
show_debug_message(node.key); // "node_d"

// node.parent - reference to "node_a4"
show_debug_message(node.parent.value); // 3
show_debug_message(node.parent.key); // "node_a4"