title: Backbone collections representing tree data
body: <p>I want to load json data in form of a tree into Backbone Collection. I can't do this. Can anyone explain what I'm doing wrong?</p>
  
  <p>My very simple model:</p>
  
  <pre><code>CTreeDataItem = Backbone.Model.extend(
  {
  });
  CTreeDataItems = Backbone.Collection.extend(
  {
      model: CTreeDataItem
  });
  </code></pre>
  
  <p>And my load attepmt:</p>
  
  <pre><code>    var treeJs =
          [
              { id: "tvRoot", title: 'Root', cssClass: 'root',
                  items: [
                      { id: "ti1", title: 'Item1', cssClass: 'item',
                          items: [
                              { id: "ti11", title: 'SubItem11', cssClass: 'subitem'},
                              { id: "ti12", title: 'SubItem12', cssClass: 'subitem'}]},
                      { id: "ti2", title: 'Item2', cssClass: 'item',},
                      { id: "ti3", title: 'Item3', cssClass: 'item', 
                          items: [
                              { id: "ti31", title: 'SubItem31', cssClass: 'subitem'},
                              { id: "ti32", title: 'SubItem32', cssClass: 'subitem'},
                              { id: "ti33", title: 'SubItem33', cssClass: 'subitem'}]}]
          }];
      this.TreeData = new CTreeDataItems();
      this.TreeData.add(treeJs);
  </code></pre>