Each auxiliary tree root has a path-parent: the parent in the original tree (not in the auxiliary tree).
class Node:
left, right: Node // children in auxiliary tree
parent: Node // parent in auxiliary tree
pathParent: Node // parent in original tree (only for aux tree roots)
value: any // node data
For non-root nodes in auxiliary tree: pathParent = null. For roots of auxiliary trees: pathParent = parent in original tree.
You can traverse up the original tree by jumping between auxiliary trees.