I grow Etoile Violette up a redbud, Venosa Violacea through a styrax, and Alionushka up a japanese maple. Just realize that any clematis growing at the base of the tree is going to need extra nutrients and moisture since it will be competing with the tree for both. Also consider the age of the tree and how big the trunk may get evenutally to help determine how far away from the tree to plant the clematis. Even if you have to plant away from the base to allow for the tree to grow, you can lead the clematis vines into the lower tree branches with a cane or long pole.

If it were me, I would allow the one on the trellis to grow into the tree and not prune it out.

One thing that I have learned is that white colored clematis or other pale colored ones show up best growing through trees and shrubs unless of course the tree or shrub has leaves that are variegated.

I grow most of my clematis through shrubs and trees. It works very well. Here is a photo of Hagley hybrid growing through a purple plum tree.

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