TERMS: node, edge, leaf, child, tree, subtree, traverse, visit

Every subtree is also a valid tree on its own.
Anything you can do to a tree, you can do to a subtree.

For HW13:  Duplicates values shall go in the right subtree.
├ In real life, it is arbitrary where you put duplicates values, but you must be consistent.
└ Sometimes you don't have separate nodes for duplicates anyway.