The following examples fails to run

http://dojo.telerik.com/UXOyu/2

when I add children to items using push.

 If I use a static object like

            data: [{
                name: "Tree",
                value: 5,
              items:[
                {
                  name:"Leaf 1"
                  value:3
                },
                {
                  name:"Leaf 2"
                  value:2
                }
                ]
            }],

 It works fine.

What am I missing?

Thanks.