Ahh. This method works in the IK Pass. That means that you probably need to call this method in “OnAnimatorIK” event instead of a regular “Update” event. To do so, please try using the Animator event node (“Events/Object/Animator”) and more specifically the “On Animator IK” port of that node, in place of the “Update” node you have now.
[attachment file=”OnAnimatorIK.png”]
Just make sure, to assign the “tree pose” animator gameobject you have in the “target” animator field of that event node’s inspector.
[attachment file=”AnimatorEventsInspector.png”]