Here is an easy paper activity to do with your classes. I got this idea from HERE. This activity could easily be done with the trees all in white and tissue in different cool colours for a fabulous winter window display - maybe next year for me!
Students first cut out the tree template from 9 X 12 inch green card stock. Then they glued pre-cut coloured strips of construction paper to one side of the tree. They trimmed off any parts that showed past the tree on the outside. They then added dots of white glue all around the template and strips and laid down a piece of green tissue paper. When dry, they carefully trimmed off the excess tissue.
I did limit the kids to 6 or 7 strips though I don't think that's necessary: however, I do recommend that they use no less than 6.