1. Set the AllowArbitraryItemHeight property of a RadTreeView to true
2. Open the RadTreeView Property Builder for that RadTreeView
3. Add an item to the root
4. Click on the item
5. Click on advanced
6. Set the ItemHeight to a custom value (e.g. 40)
7. Click apply
8. Reopen the Property Builder - you will notice that the ItemHeight value is reset.