It is important that it removes up to and including the specified depth
because the stack is used when doing depth first search. Each call to
popUntil is expected to remove a layer. New nodes are then added to the
parent which is the first one from the previous layer.
It is important that it removes up to and including the specified depth because the stack is used when doing depth first search. Each call to popUntil is expected to remove a layer. New nodes are then added to the parent which is the first one from the previous layer.