hi,
maybe you should put your christmas tree up a couple of days before christmas. then maybe your cat won't have time to tear it down. you might have to rush to put it up instead of taking your time with it. but it might also work. you could always try it. Also you might want to get a fake tree and use ornaments that won't break. or when your cat gets close to the tree you can spray it with water so it will learn not to go near the tree.
-sam-