Train the cat to stay away from it--it is easy to do, and you've had excellent suggestions here. We trained our kitten last Christmas, and this year he is sleeping peacefully underneath the tree, looking like a Norman Rockwell print.

If you aren't going to take responsibility for training your animals, you shouldn't be a pet owner. Kittens can easily be trained to stay away from the Christmas tree, but it takes a knowledgeable, committed, consistent owner. If you aren't willing to do all that is necessary to own a pet, maybe you should seriously consider finding a new owner for the kitten who will take the responsibility seriously.