Currently, setting HierarchyIndent property does not work as expected for nested rows.
Reproducible on http://demos.telerik.com/silverlight/#TreeListView/TreeListViewDragAndDrop
As a workaround you can try executing the selection in a Dispatcher with DispatcherPriority.Render. This may not apply in the case when there are many nodes outside the View area.
The goal is to expand a second node each time you expand a particular node from the RadTreeListView. The data of the second node is loaded on demand, but it is not shown when the node itself is expanded.