I was just out walking around the neighborhood and I realized that trees tend to place their leaves on the outer periphery of the branches. It forms a canopy—which, I guess is why we use the same word for a forest's treetops and a kind of roof.
I think this is what is making my tree models look so weird and sparse. I think I can string ropes to form a kind of quasi-organic geodesic dome that would provide the hooks upon which to attach the leaves. That was another sticking point in the design: how to create nodes where one could hang jeir message. I was pondering making some kind of wooden branches, but they'd be likely to snap in high winds.