The best way to secure a Christmas tree from cats is to place it in a sturdy tree stand that is difficult for cats to knock over. You can also use a tree skirt or netting around the base of the tree to prevent cats from climbing up the tree. If your cat is particularly mischievous, you may also want to consider using a spray deterrent to keep cats away from the tree. Additionally, you can place physical barriers such as baby gates around the tree or install a cat fence to keep cats out of the room with the tree.