Trish was 11 months old for her first Christmas and we also had a kitten at that time. I was constantly dragging her out from under the tree and the cat out of it. After it fell over for the second time from the kid and the cat, I finally took it down and put what was left of the ornaments on a little artificial tree that I could sit on a table out of their reach.
When Jami and Bubbie were little it was a wild even without a decorated tree. After I'd put it up for about the third time I finally sat in the middle of my living room crying like a baby. Then something came to me. They could escape from everything, the playpen, their cribs, strollers and carseats, so I opened up the playpen (it was one of those wooden ones with bars) put the tree and the packages inside the playpen and it stayed safe! It seems they could climb out but not in!