There is a cute tree and ornament PDF you could use (I already had one from a previous music leader) at http://sunbeamsinging.wordpress.com/2012/11/24/trim-a-tree/.
(no, this is not my tree, but it should give you an idea)
I talked to the kids for a minute about the origins of Christmas trees, and how we use evergreen trees to symbolize eternal life. I encouraged them to remember this when they looked at their Christmas tree, and to remember the gift Jesus gave us.
I also told them that in other countries, the Christmas tree isn't decorated until Christmas Eve, so since we were meeting on the 23rd I figured it was close enough and we could decorate a couple.
The bare laminate tree was posted on the board, and the ornaments (with songs written on the back) around the room. I picked a child to pick an ornament, put it on the laminated tree, and we would sing the Christmas song on the back. Then (assuming they sang well), I would call one or two kids up to help decorate the mini tree. We used battery-operated lights, tinsel, tiny ornaments, and tiny foil-wrapped gifts. They just loved that everything was so tiny, and between the two trees just about everyone got a turn!!!