How to use the voila.treehandler.VoilaTreeHandler function in voila

handlers.append((
                url_path_join(self.server_url, r'/(.*)'),
                VoilaHandler,
                {
                    'notebook_path': os.path.relpath(self.notebook_path, self.root_dir),
                    'nbconvert_template_paths': self.nbconvert_template_paths,
                    'config': self.config,
                    'voila_configuration': self.voila_configuration
                }
            ))
        else:
            self.log.debug('serving directory: %r', self.root_dir)
            handlers.extend([
                (self.server_url, VoilaTreeHandler, tree_handler_conf),
                (url_path_join(self.server_url, r'/voila/tree' + path_regex),
                 VoilaTreeHandler, tree_handler_conf),
                (url_path_join(self.server_url, r'/voila/render/(.*)'),
                 VoilaHandler,
                 {
                     'nbconvert_template_paths': self.nbconvert_template_paths,
                     'config': self.config,
                     'voila_configuration': self.voila_configuration
                 }),
            ])

        self.app.add_handlers('.*$', handlers)
        self.listen()

env.install_gettext_translations(nbui, newstyle=False)

    host_pattern = '.*$'
    base_url = url_path_join(web_app.settings['base_url'])

    tree_handler_conf = {
        'voila_configuration': voila_configuration
    }
    web_app.add_handlers(host_pattern, [
        (url_path_join(base_url, '/voila/render/(.*)'), VoilaHandler, {
            'config': server_app.config,
            'nbconvert_template_paths': nbconvert_template_paths,
            'voila_configuration': voila_configuration
        }),
        (url_path_join(base_url, '/voila'), VoilaTreeHandler, tree_handler_conf),
        (url_path_join(base_url, '/voila/tree' + path_regex), VoilaTreeHandler, tree_handler_conf),
        (url_path_join(base_url, '/voila/static/(.*)'), MultiStaticFileHandler, {'paths': static_paths}),
        (
            url_path_join(base_url, r'/voila/files/(.*)'),
            WhiteListFileHandler,
            {
                'whitelist': voila_configuration.file_whitelist,
                'blacklist': voila_configuration.file_blacklist,
                'path': os.path.expanduser(web_app.settings['server_root_dir']),
            },
        ),
    ])

    # Serving notebook extensions
    if voila_configuration.enable_nbextensions:
        # First look into 'nbextensions_path' configuration key (classic notebook)
        # and fall back to default path for nbextensions (jupyter server).