_includes/themes/zeppelin/sideMenu.html

<div class="row">
  {% if page.menu %}
    <div class="sideMenu col-sm-3">
      {% assign pages_list = site.pages %}
      {% assign group = page.menu %}
      {% include JB/pages_list %}
    </div>
    <div class="col-sm-9">
      {{ content }}
    </div>
  {% else %}
    <div class="col-sm-12">
      {{ content }}
    </div>
  {% endif %}
</div>