I have this basic tutorial script from the documentation...
func _ready():
var tree = Tree.new()
var root = tree.create_item() # Here the 1st TreeItem is returned to root
tree.set_hide_root(true)
var child1 = tree.create_item(root)
var child2 = tree.create_item(root)
var subchild1 = tree.create_item(child1)
The TreeItem inherits from Object and not from Node so I suppose I cannot add a custom Control node (and its children) to the tree!?
Wouldn't this be a useful feature? :)