The best way to keep your cat out of the Christmas tree is to make the tree as unappealing to them as possible. This can be done by wrapping the tree in a protective mesh or foil, using deterrent sprays, or placing a tall object around the tree to block your cat's access. You can also provide alternative sources of entertainment and attention for your cat, such as toys and games, to divert their focus away from the tree. Additionally, make sure to keep the tree well-watered, as cats may be drawn to the fresh water and try to drink from it.