I do this lesson with my first graders. First we use tempera cakes to paint a sky and grass landscape on a 9x12 piece of white paper. Students get a second piece of paper (it can be 6x9 or smaller) and on this paper they are instructed to paint it reds, yellows and oranges. The second week, the students cut out a tree trunk from brown paper and I tell them it can't be a straight rectangle. (This example actually had a nice Y shape at the top but it got covered with her leaves.) After the trunk is glued to the paper, they cut up their red/orange paper for leaves.