A '''Nest''' is a specific arrangement of a [[trio]] of pyramids, namely a [[stack]] with a [[large piece]] on top, a [[medium piece]] in the middle, and a [[small piece]] on the bottom. The hollow [[Icehouse piece]]s are designed so that each piece fits neatly inside another piece of the next larger [[size]]. The three-piece stack complementary to the Nest is the [[Tree]].
It is probably an accidental verity that you can put a Nest in your Tree, but you can't put a Tree in your Nest.