It is a coincidence that my son is working with this exact situation. I provided some inclusion (and he is getting it) but not too heavy. Generally though, with many of these things, exclusion applies. We can technically gather up everything and build a tree but I find that in a natural setting one thinks more often in an exclusive fashion because it partitions and balances the knowledge more effectively. It's all the leaves gathered on each of the branches that we work with. Not so much the bare tree.