{% load catalogue_tags %}

{% book_tree orphans books_by_parent %}
{% for author, group in books_by_author.items %}
  {% if group %}
    <a name="{{ author.slug }}"></a>
    <div class="group">
      <h2><a href="{{ author.get_absolute_url }}">{{ author }}</a></h2>
      {% book_tree group books_by_parent %}
    </div>
  {% endif %}
{% endfor %}