code: def expandtree(self, model=None):
          
          if model and not self.columns:
              schema = model.schema()
              defaults = schema.columns(flags=orb.Column.Flags.AutoExpand).keys()
              defaults += schema.collectors(flags=orb.Collector.Flags.AutoExpand).keys()
          else:
              defaults = []
  
          expand = self.expand or defaults
          if not expand:
              return {}
  
          def build_tree(parts, tree):
              tree.setdefault(parts[0], {})
              if len(parts) > 1:
                  build_tree(parts[1:], tree[parts[0]])
  
          tree = {}
          for branch in expand:
              build_tree(branch.split('.'), tree)
  
          return tree
docs: Goes through the expand options associated with this context and
          returns a trie of data.
  
          :param model: subclass of <orb.Model> || None
  
          :return: <dict>