The best way to keep cats away from the Christmas tree is to make it unappealing for them. Cats love to climb and explore, so you can try to put up barriers around the base of the tree or put some tinsel or other decorations that are toxic to cats on the lower branches to deter them. You can also try spraying the tree with a scent that cats don't like, such as citrus or vinegar. Finally, you can try offering the cats a more attractive alternative to the tree, such as a scratching post or a bed they can play and nap on.