title: How to add checkboxes to Ext.tree.TreePanel?
body: <p>I created this simple tree:</p>
  
  <pre><code>var children = [{
           text:'My Layers',
           children:[
             new Ext.tree.TreeNode({text:'test1',leaf:true}),
             new Ext.tree.TreeNode({text:'test2',leaf:true})
          ]
      }];
      var tree = new Ext.tree.TreePanel({
         loader:new Ext.tree.TreeLoader(),
         width:150,
         title:'Layers',
         height:250,
         collapsible:true,
         rootVisible:false,
         root: new Ext.tree.AsyncTreeNode({
             expanded:true,
             leaf:false,
             text:'Tree Root',
             children:children
         })
      });
  </code></pre>
  
  <p>How can I add a Checkbox to each node?</p>
  
  <p>Actually I'm gonna pass the list as a parameter to the function in a JSON array (e.g. ["test1","test2"]). What is the proper way to load nodes from JSON data?</p>
  
  <p>I'm using ExtJs 2.3 with GeoExt.</p>
  
  <p>Cheers!</p>