WordPress投稿画面のタグをカテゴリーのようにチェックボックスに変更する方法

function post_tag_checkbox() {
  global $wp_rewrite;
  $rewrite = array(
    'slug' => get_option('tag_base') ? get_option('tag_base') : 'tag',
    'with_front' => !get_option('tag_base') || $wp_rewrite->using_index_permalinks(),
    'ep_mask' => EP_TAGS,
  );

  $labels = array(
    'name' => _x('Tags', 'taxonomy general name'),
    'singular_name' => _x('Tag', 'taxonomy singular name'),
    'search_items' => __('Search Tags'),
    'popular_items' => __('Popular Tags'),
    'all_items' => __('All Tags'),
    'parent_item' => null,
    'parent_item_colon' => null,
    'edit_item' => __('Edit Tag'),
    'view_item' => __('View Tag'),
    'update_item' => __('Update Tag'),
    'add_new_item' => __('Add New Tag'),
    'new_item_name' => __('New Tag Name'),
    'separate_items_with_commas' => __('Separate tags with commas'),
    'add_or_remove_items' => __('Add or remove tags'),
    'choose_from_most_used' => __('Choose from the most used tags'),
    'not_found' => __('No tags found.')
  );

  register_taxonomy('post_tag', 'post', array(
    'hierarchical' => true,
    'query_var' => 'tag',
    'rewrite' => $rewrite,
    'public' => true,
    'show_ui' => true,
    'show_admin_column' => true,
    '_builtin' => true,
    'labels' => $labels
  ));
}
add_action('init', 'post_tag_checkbox');