We used a paint on a pallet, putting a glob of green paint on a paper plate and smearing it around with Ethan's little hand before we "smack smack smacked" it down on the paper. (Saying "smack smack smack" makes it quite fun for your little person!) Since making the snowman handprint ornament, I've found the paper plate is really effective if you need to make a number of handprints!
After we got the tree shape done, we used different colored paint on his fingertips to create the lights and then I helped him smear paint into a tree trunk.
When we were all done, Ethan asked for more paper and to my surprise, he made a second tree by himself (it's one of those modern upside down types)! When he was done, he pulled the page off of his tray and pointed for me to hang it up to dry next to the tree we had done together. "Is that a Christmas Tree?" "Christmas Tree- uh huh!" Great look through the eyes of a toddler! Well done little dude. :)