The human brain is often described as the most complex object in the universe. Tens of billions of nerve cells-tiny tree-like structures—make up a massive network with enormous computational power. -- Trees of the Brain, Roots of the Mind

Our thoughts literally flow through and exist as tree structures. In the sense that we are the thing that is aware, we are each great forests of neurons. It does not necessarily follow that mapping the world in the form of tree-like hierarchies is conducive to thought but it is suggestive.

As social animals we are bred to be exquisitely sensitive to dominance hierarchies in families and tribes. The less sensitive stumble in the mating dance. The survivors of eons of such selection are good at remembering hierarchies.

The typical Memory Palace works by associating objects with our spacial memory. We seem to have a separate set of registers for recording dominance hierarchies, available for use as a separate memory palace channel.