开始很容易。让我们获取2015年的所有帖子：

$posts = new WP_Query( \'year=2015\' );

现在，我们有一个post对象数组，我们必须将其分类，如果它们有多个类别，则复制它们。结果进入多维数组。

$categorized_posts = array ();
foreach ($posts as $post) {
  $post_cats = wp_get_post_categories ($post->ID, array(\'fields\' => names));
  foreach ($post_cats as $post_cat) {
    $categorized_posts[$postcat][] = $post->ID;
    }
  }

所以$categorized_posts 是一个具有类别名称的数组，对于每个类别名称，都有一个对应帖子的ID数组。缺少的是层次结构树。我们将循环浏览所有类别，并将它们与相应的帖子标题一起打印。为了按层次进行此操作，我们使用the recursive function found here, 我们对其进行修改以输出帖子标题。

// this goes in the template where you want the tree to be printed
wpse237979_hierarchical_category_tree (0, $categorized_posts );

// this goes in functions.php
function wpse237979_hierarchical_category_tree ( $cat, $categorized_posts ) {
  $next = get_categories(\'hide_empty=false&orderby=name&order=ASC&parent=\' . $cat);
  if ($next) {    
    foreach ($next as $cat) {
      if (array_key_exists($cat,$categorized_posts)) {
        echo \'<ul><li><strong>\' . $cat->name . \'</strong>\';
        // now loop through the gathered ID\'s of posts belonging to this category
        $current_cat_posts = $categorized_posts[$cat];
        foreach ($current_cat_posts as $current_cat_post) {
          $this_post = get_post ($current_cat_post);
          echo \'<h2>\' . $this_post->post_title . \'<h2>\';
          }
        }
    wpse237979_hierarchical_category_tree( $cat->term_id, $categorized_posts );
    }   
  }
  echo \'</li></ul>\'; echo "\\n";
} 

注意：我并没有实际测试这段代码，所以可能需要进行一些调试，但我相信您已经了解了总体思路。