Hello Jerzy Rzaniak,
I see now. We are not supporting this scenario. The TreeView control is an ItemsControl which binds to ItemCollection. You need to manually build an hierarchical collection out of your self-referencing data and then to bind that collection to the RadTreeView.
To build a hierarchical collection you can use LINQ. Check this article on how to implement this:
Let us know if you need more help on implementing that.
the Telerik team
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