code: def _build_toctree(self):
          
          dirname = posixpath.dirname(self._env.docname)
          tree_prefix = self.options['toctree'].strip()
          root = posixpath.normpath(posixpath.join(dirname, tree_prefix))
          docnames = [docname for docname in self._env.found_docs
                      if docname.startswith(root)]
  
          # Sort docnames alphabetically based on **class** name.
          # The standard we assume is that task doc pages are named after
          # their Python namespace.
          # NOTE: this ordering only applies to the toctree; the visual ordering
          # is set by `process_task_topic_list`.
          # NOTE: docnames are **always** POSIX-like paths
          class_names = [docname.split('/')[-1].split('.')[-1]
                         for docname in docnames]
          docnames = [docname for docname, _ in
                      sorted(zip(docnames, class_names),
                             key=lambda pair: pair[1])]
  
          tocnode = sphinx.addnodes.toctree()
          tocnode['includefiles'] = docnames
          tocnode['entries'] = [(None, docname) for docname in docnames]
          tocnode['maxdepth'] = -1
          tocnode['glob'] = None
          tocnode['hidden'] = True
  
          return tocnode
docs: Create a hidden toctree node with the contents of a directory
          prefixed by the directory name specified by the `toctree` directive
          option.