title: Bootstrap grid make a column expand under its neighbor column
body: <p>Hi guys its hard to put this in english so here is the drawing of the layout I want to accomplish. I don't know if this is possible in Bootstrap grid system only.</p>
  
  <pre><code>&lt;div class="row"&gt;
     &lt;div class="col-md-6" id="col1"&gt;... children &lt;/div&gt;
     &lt;div class="col-md-6" id="col2"&gt;... children &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/HB6XI.png" alt="drawing of the layout"></p>