One way to keep a cat from climbing the Christmas tree is to create a barrier around it using aluminum foil or double-sided tape. The sound and texture of the foil or tape will deter the cat from getting close to the tree. Another option is to place the tree in a corner or near a wall, which will make it harder for the cat to climb. Additionally, providing the cat with alternative places to climb and play, such as a cat tree or scratching post, can also help keep them from climbing the Christmas tree.