Questions 11.9 from the course text.
|M||
/ \
/ \
|D|I| |S||
/ | \ / \
/ | \ / \
|B|| |G|| |K|| |P|| |U||
/ \ / \ / \ / \ / \
|A|| |C|| |E|| |H|| |J|| |L|| |N|O| |R|| |T|| |W||