/**
 * Tree view : a simple tree view
 */
function groups_admin_tree_view()
{
    global $wpdb;
    $output = '';
    $today = date('Y-m-d', time());
    if (!current_user_can(GROUPS_ACCESS_GROUPS)) {
        wp_die(__('Access denied.', GROUPS_PLUGIN_DOMAIN));
    }
    $output .= '<div class="groups-tree-view">' . '<h1>' . __('Tree of Groups', GROUPS_PLUGIN_DOMAIN) . '</h1>';
    $tree = Groups_Utility::get_group_tree();
    $tree_output = '';
    Groups_Utility::render_group_tree($tree, $tree_output);
    $output .= $tree_output;
    $output .= '</div>';
    // .groups-tree-view
    echo $output;
}