Return the dependencies as a TreeMap.

        Returns:
            TreeMap: instance of TreeMap.

def as_treemap(self):
        """
        Return the dependencies as a TreeMap.

        Returns:
            TreeMap: instance of TreeMap.
        """
        if self._treemap_cache:
            return self._treemap_cache
        self._treemap_cache = treemap = TreeMap(self)
        return treemap