If there are no children in treeview node, then there must not by any plus sign. Why you show plus sign ? i dont understand. No children nodes cannot expand.
In the current version (2010 Q3 SP1) of the RadTreeView the +- symbols do not show on nodes that don't have children (see screenshot).
I'd also like to let you know that there is a brand new RadTreeView that is due out in the following Q1 2011 release that is due the middle of this month.
I hope this helps but let me know if you have any questions
Richard