The problem is that you are using the domElement of the RadTreeView and you are trying to call the commitChanges()
method from there.
tree = document.getElementById(
You need to work with the client-side object found this way:
"<%= RadTreeView1.ClientID %>"
Also in the code you provided I see you are working with the private fields of the RadTreeView:
However this is not appropriate because if we change something in this fields your code will stop working. I'll suggest you to use the public propeties as described in this help topic
Please let me know if you have further questions.
All the best,
the Telerik team
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