I went to the Disney Outlet yesterday and they have some Christmas Ornaments on sale.
You could make ornaments using pictures of your past trips as well as some Disney Ornaments.

Give it a personal touch (other then
disney store ornaments). Also a stuffed mickey as an angel is not bad either.
If you have a trip coming up, you could always use the tree as a count down. Like put numbers going down the tree. Or daily pictures count down with you and your family holding a sign saying " 3 days to go" looking silly.