The horizontal scrollbar of RadTreeListView is displayed even the setup suggest that it should not be. For example, this happens if you have a single column with its Width set to * which means that the RadGridView should span in the available space without the need of displaying a horizontal scrollbar. To recreate this the RowIndicatorVisibility property should be set to Collapsed. Additional to that there should be a hierarchy and the items should be expanded.

To work this around, you can set a fixed Width for the column. If you want this to be dynamic you can calculate the width on SizeChanged of RadTreeListView