You know, I've heard of a few tricks to keep cats from climbing on the Christmas tree. One is to wrap the base of the tree in aluminum foil. Cats don't like the sound it makes when they touch it and they usually avoid it. Another trick is to place a few empty boxes around the tree. Cats love to explore and they'll probably be more interested in the boxes than the tree. You could also try hanging some colorful ribbons from the branches. Cats are attracted to movement, so the ribbons will probably keep their attention away from the tree.