title: A hierarchy in CheckBoxList
body: <p>I have 2 tables, Categories and Sub Categories. Is it prossible to present all sub categories in a checkbox list arraged by their cagetories? </p>
  
  <p>Something like this:</p>
  
  <p>Category 1</p>
  
  <ul>
  <li>sub category checkbox1</li>
  <li>sub category checkbox2</li>
  </ul>
  
  <p>Category 2</p>
  
  <ul>
  <li>sub category checkbox3</li>
  <li>sub category checkbox4</li>
  </ul>
  
  <p>Category 3</p>
  
  <ul>
  <li>sub category checbox5</li>
  </ul>