I found this phenomenal project in Dynamic Art Projects for Children, which someone got me as a gift when I was in grad school. It is an extremely successful lesson!
I love how excited the fourth grade students get to learn about the The Great Banyan Tree in India. We discuss why the Banyan tree might be the national tree there, and how it symbolizes unity to them because they gather under the shade it provides. I also played them this video that basically blew their minds when they considered that what they were seeing was ALL ONE TREE!