One of the most effective ways to keep a cat from eating a Christmas tree is to provide them with an alternative source of entertainment. A cat tree or scratching post can keep them busy and away from the tree. Additionally, you can try placing a cat repellent around the base of the tree. Make sure to supervise the cat around the tree and remove any decorations that may be hazardous. With a little extra care and attention, you can keep your cat safe and the tree intact.