Use chicken wire to encourage a Clematis (or other vine) to clamber up a tree. HOWEVER - be careful to leave some room for the tree trunk to grow thicker, check it every year, and don& plant an aggressive vine that might strangle the tree.
i love wisteria. when i was growing up, my grandparents had a huge bush of wisteria in their front yard, and it was always so beautiful in the spring, and smelled good, too! i miss them and that wisteria bush.