What is your reasoning behind cliping the way you do on the right? Sure, if you make sure the carabiner is not contacting anything AND you stand right by it to make sure it doesn't shift, its fine.

However, most of the time, you can go directly through the knot(still keep direction of pull in mind). Otherwise, you could use a bowline and tie off the tree or a basket hitch, which doesn't have the problem of cinching down and risking contacting the tree. Incidentally, I'm going more and more to a basket hitch because I feel it is better for the tree.