Is it possible to sort by a materialized path tree's `path` text field in order to find the right-most node of the tree? For example, consider this python function that uses django-treebeard's `MP_Node`:

```python
def get_rightmost_node():
    """Returns the rightmost node in the current tree.

    :rtype: MyNode
    """
    # MyNode is a subclass of django-treebeard's MP_Node.
    return MyNode.objects.order_by('-path').first()

```

From all my testing, it seems to return what I expect, but I don't know how to come up with the math to prove it. And I haven't found any info on performing this operation on a materialized path tree.

Treebeard's implementation doesn't have separators in paths, so the paths
look like this: `0001`, `00010001`, `000100010012`, etc.