Since getting Paizly we've only put the tree up a few times (we've had her for four years) and once we never even decorated it! I believe it was 2010 that we didn't do a tree because Jax was a kitten.
We put our tree up this weekend and all the cats did was eat it. When I catch them I squirt them (which I was always opposed to doing, but it works and I don't do it hardly ever) or stomp on the ground (which usually doesn't phase them). At least Paizly isn't climbing in it like she did when she was a kitten.
I told my boyfriend my goal this year was to have ZERO broken ornaments. I know he is going to be the one to break one! Not the cats! LOL
If the cats are causing a huge problem, the only thing I could suggest is to not put it up. I know that's sad, but it would make things less stressful for everyone. Maybe like others suggested, get a small one and put it up on something where the cats do not have a way of getting to it.