Nice, elegant tree. Although it is limited to a pair-structure.

In many cases I don't have an ordered tree structure. When I create a procedural dungeon I start with distributing rooms and then write a function that walks between the rooms, to establish which pathways and squares are most commonly accessed, without the hindrance of walls. Next I write a function that transforms the array of walking patterns into corridors connecting the rooms. Procedurally generated obstacles that prevent direct walking from point A to B can help making the dungeon less linear. This could represent areas of rock that was too hard to cut through. The testing functions are ad-hoc trees that explore the dungeon and branch when necessary, then pruned as the "explorers" hit a dead end.