There are several ways to keep cats out of your Christmas tree. One method is to use a tree skirt or a sheet to cover the bottom of the tree and keep your cat from climbing it. Another way is to use a deterrent spray that cats find unpleasant, such as bitter apple or citrus oil. Additionally, you can place aluminum foil around the bottom of the tree, as cats don't like the crinkly sound it makes when they touch it. You could also consider getting a tree that is taller and harder for your cat to climb.