They return the left and right most nodes of the entire tree, i.e.
starting from the root node.
Change-Id: I651a9db6d12308aef4c2ed71484958428e58c9bc
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2838
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
621f53700f