<?php
    // use wp_list_pages to display parent and all child pages all generations (a tree with parent)
    $parent = $post->ID;
    $args=array(
      'child_of' => $parent
    );
    $pages = get_pages($args);
    if ($pages) {
      $pageids = array();
      foreach ($pages as $page) {
        $pageids[]= $page->ID;
      }

      $args=array(
        'include' =>  $parent . ',' . implode(",", $pageids)
      );
      wp_list_pages($args);
    }
    ?>