im guessing you mean the built in treeview control? in short no although you could have a fiddle with the CSS that is generated in the background. I would warn against using it though as having tried to use it in previous projects it is very slow, cumbersome and if you have anywhere near verging on 100 nodes or more will probably kill your viewstate.

That said if you have no qualms with using a javascript treeview (on the client) try the Yahoo UI library.

Al Salam Alikom,
I have a simple solution:
Create a table from a single cell and put your treeview in this cell
then go to the properties of this cell you will find an attribute "Dir",
assign it to "rtl" .
I wish this this solve your problem.