title: Angular JS subgroups in ng-option
body: <p>Does anyone know how to get sub-groups in an ng-option list. I have a query that looks something like this that works fine.</p>
  
  <pre><code>l.symbol as l.description group by l.country for l in locations
  </code></pre>
  
  <p>but I would ideally like to do this which does not work:</p>
  
  <pre><code>l.symbol as l.description group by [l.region, l.country] for l in locations
  </code></pre>
  
  <p>the expected result in the dropdown that I am after would then look like this:</p>
  
  <pre><code>AMER
    CANADA
      MONTREAL
      TORONTO
    USA
      CHICAGO
      NEW YORK
  APAC
    China
      Bejing
      Shanghai
    Japan
      Kyoto
      Tokyo
  </code></pre>
  
  <p>Is this even possible out of the box?</p>