我通过修改问题中链接的函数使其递归来解决这个问题。注释解释了我的更改：

function woocommerce_subcats_from_parentcat_by_ID( $parent_cat_ID ) {
$args = array(
   \'hierarchical\' => 1,
   \'show_option_none\' => \'\',
   \'hide_empty\' => 0,
   \'parent\' => $parent_cat_ID,
   \'taxonomy\' => \'product_cat\'
);
$subcats = get_categories($args);

if ( $subcats ) { // added if statement to check if there are subcategories
  echo \'<ul class="product-category-list">\';
    foreach ($subcats as $sc) {
      $link = get_term_link( $sc->slug, $sc->taxonomy );
        echo \'<li><a href="\'. $link .\'">\'.$sc->name.\'</a></li>\';
        woocommerce_subcats_from_parentcat_by_ID( $sc->term_id ); // function calls itself
    }
  echo \'</ul>\';
} else {
  return; //return if no subcategories
    }} // last bracket kept being pushed out of code block if I used a line break