Appending a child with children in node interface

Hi,

I used to append a child that contained children in the extjs4 and it worked. Now it doesn't! Here is an example:

Code:

new Ext.tree.Panel({    renderTo: document.body,
    width: 300,
    height: 300,
    title: 'rootchange Event Test',
    store: {
        root: {
            text: 'Root',
            expanded: true,
            children: [{
                text: 'Foo',
                leaf: true
            }]
        }
    },
    dockedItems: [{
        xtype: 'toolbar',
        dock: 'top',
        items: [{
            text: 'appendChild',
            handler: function(button) {
                var tree = button.up('treepanel'),
                    store = tree.getStore(),
                    root = store.getRootNode();
                
                root.appendChild({
                    text: 'Bar',
                    expanded: true,
                    children: [{
                        text: 'Baz',
                        leaf: true
                    }]
                });
                
                
            }
        }]
    }]
});

Regards,

Paul