How do I get my cats to stop messing with the Christmas tree?

Spray them with a squirt bottle. I have two, one in the living room and one in the bedroom. My two kittens have learned not to be around the tree. You can find them in the aisle of Walmart with all the travel size shampoo, soap, etc. I squirt them whenever they do/get into anything I don't want them to. It works well for the most part, but they still repeat it eventually.