Thanks for not replying my post.
I fixed this by adding this CSS properties in my own code:
:root .RadTreeView_rtl .rtPlus, :root .RadTreeView_rtl .rtMinus
margin-left: 7px !important;
margin-right: -18px !important;
right: 0 !important;
One of my colleges found out this is something to do with fixing something in opera in Telerik source code.
Anyway this was really disappointing ...