The best way to keep cats away from the Christmas tree is to put some deterrents in place. You could try spraying the tree with a mixture of water and white vinegar, as cats don't like the smell of vinegar. You could also try placing aluminum foil around the base of the tree to make it less appealing to cats, or try placing sticky tape on the branches to deter them from climbing. Finally, you could try placing a few citrus scents around the tree, as cats don't like the smell of citrus.