title: How to create tree view with checkboxes in extjs4
body: <p>I am working in Extjs4. I want to create tree view with checkBoxes for selection of individual entry.
  I have json as-</p>
  
  <pre><code>{"data":[{"Maincategory":"Main","maincategoryId":"1","Subcategory":{"subcategory":"GK","categoryId":"2"},{"subcategory":"History","categoryId":"3"},{"subcategory":"Geography","categoryId":"4"}]},{"Maincategory":"GK","maincategoryId":"2","Subcategory":[{"subcategory":"environment","categoryId":"5"}]},{"Maincategory":"History","maincategoryId":"3","Subcategory":[{"subcategory":"civics","categoryId":"7"}]},{"Maincategory":"Geography","maincategoryId":"4","Subcategory":[{"subcategory":"India","categoryId":"8"}]},{"Maincategory":"environment","maincategoryId":"5","Subcategory":[]}]}
  </code></pre>
  
  <p>i want to create tree view of this json. So how to create tree view with checkboxes in extjs4.</p>