add a few things:

* test case with folders/subfolders
* renaming items by double-clicking them
* naive drag test

ControlTreeItem.tscn

@@ -1,6 +1,8 @@
-[gd_scene load_steps=2 format=2]
+[gd_scene load_steps=4 format=2]
 
 [ext_resource path="res://ControlTreeItem.gd" type="Script" id=1]
+[ext_resource path="res://DragHandle.gd" type="Script" id=2]
+[ext_resource path="res://RenamableButton.gd" type="Script" id=3]
 
 [node name="ControlTreeItem" type="VBoxContainer"]
 anchor_right = 0.479
@@ -39,6 +41,7 @@ unique_name_in_owner = true
 margin_right = 32.0
 margin_bottom = 32.0
 rect_min_size = Vector2( 32, 0 )
+script = ExtResource( 2 )
 
 [node name="CheckBox" type="CheckBox" parent="ItemAtom"]
 unique_name_in_owner = true
@@ -56,6 +59,7 @@ toggle_mode = true
 text = "Item text"
 flat = true
 align = 0
+script = ExtResource( 3 )
 
 [node name="Subitems" type="VBoxContainer" parent="."]
 unique_name_in_owner = true