My cat Delores has broken so many ornaments over the past few years that I completely gave up on having a full size tree and I just keep a desktop artificial tree near my computer. I don't know what makes cats go crazy and want to jump on, climb and even chew on natural Christmas trees. But I don't want to pick up any more broken glass or pick up a tree that's been knocked over, so I'll just be doing the little fake tree from now on. I used to use tinsel and I never had problems with my cat eating it but she did like to play with it and I would find tinsel all over the carpet.
Delores likes to chew on cords, which is bad news when it comes to Christmas lights and I worry that one day she'll get electrocuted. Cats are great pets, but they can be a handful around the holidays and I don't decorate as much as I used to.