code: def tree_structures_for(self, prefix, current_oid, parent_oids, prefixes):
          
          if prefix and prefixes and prefix not in prefixes:
              return empty, empty
  
          parent_files = set()
          for oid in parent_oids:
              parent_files.update(self.entries_in_tree_oid(prefix, oid))
  
          current_files = self.entries_in_tree_oid(prefix, current_oid)
          return (current_files, parent_files), (current_files - parent_files)
docs: Return the entries for this commit, the entries of the parent commits,
          and the difference between the two (current_files - parent_files)