Our cats always, always knocked the tree over. They would wait, until we went to bed. Then we would hear a Christmas ball or two, hit the floor. Then Swoosh, the whole tree came down. Eventually, I put anchor's in the wall, and tied it.
Our cat, over it’s 12 year life, never bothered our tree. She would sleep under tree on occasion and often sit and stare at tree but that’s it —- go figure.