Are you using the Site Treeview control for your navigation? You mentioned the results you're looking for, but what is the Treeview currently displaying?
I suspect what you're wanting is to select the starting node. The Site Treeview control does not currently allow this. However, you can create a custom control to do this fairly easily.
The following thread explains how to create this control:http://www.sitefinity.com/support/forums/support-forum-thread/b1043S-bgatdc.aspx
Hopefully this is what you're looking. Please let me know if this does not help.