这已经得到了回答here

这两个循环都需要存在，您可以随意显示它。

foreach( get_terms( \'products-category\', array( \'hide_empty\' => false, \'parent\' => 0 ) ) as $parent_term ) {
  // display top level term name
  echo $parent_term->name . \'<br>\';

  foreach( get_terms( \'products-category\', array( \'hide_empty\' => false, \'parent\' => $parent_term->term_id ) ) as $child_term ) {
    // display name of all childs of the parent term
    echo $child_term->name . \'<br>\';
  }

}