The X coordinate of the position of a TreeNodeUI object is:
The bounds of the TreeNodeUI objects are in client coordinates, i.e. relative to the tree view control.
However, you should not need to offset the bounding rectangle, because it does not contain the area of the expand/collapse button (because it is represented by a different object). I tested again the code in my response and I could collapse the node by clicking on the expand/collapse button.
So, please try without offsetting the bounding rectangle. If it does not work I will need some more information about your case - for example what your structure of nodes looks like.
the Telerik team
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