docs: def _gen_etetoolkit_tree(self, node, subject_info_tree):
          """Copy SubjectInfoTree to a ETE Tree."""
          for si_node in subject_info_tree.child_list:
              if si_node.type_str == TYPE_NODE_TAG:
                  child = self._add_type_node(node, si_node.label_str)
              elif si_node.type_str == SUBJECT_NODE_TAG:
                  child = self._add_subject_node(node, si_node.label_str)
              else:
                  raise AssertionError(
                      'Unknown node type. type_str="{}"'.format(si_node.type_str)
                  )
              self._gen_etetoolkit_tree(child, si_node)