You can use VisualTreeHelper.GetChild method to get the visuals from the RadTreeViewItem template but this is not the recomended way.
The good way is to inherit RadTreeViewItem add some properties to hold your data, modify the RadTreeViewItem template to include your control and bind it to your data property. Or the easier way is to put the your data into RadTreeViewItem Tag
property and bind your control to the Tag
prop but this has some limitation.
If you have more questions, I'll be glad to help.
the Telerik team
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