This is actually a key part of #60, because it means that in many cases we don't need to generate the full stop tree graph, but just the root, or the ancestors of a certain base.
Need to consider if we should we assume (as is currently the case) that stations can only have a child or a parent as a station but not a grandparent or grandchild.
This is actually a key part of #60, because it means that in many cases we don't need to generate the full stop tree graph, but just the root, or the ancestors of a certain base.