Perhaps you are expanding the TreeVIew in an ajax request?
If this is the case and the Button is still not visible, then most likely to me is that the button is not updated in this same request. This means that if you use panels (RadAjaxPanel or UpdatePanel) the TreeView and the button are not in the same panel, or if you use RadAjaxManager, the TreeView (as control triggering update), does not include the button as an UpdatedControl.
Could you, please, share a full page reproducing this behavior?
the Telerik team
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