Showing loading icon on ExtJs 4.1.1 tree panels node when expanded

Question

I am using ExtJs 4.1.1 tree panel.

  xtype: 'treepanel',
                 id: 'tPanel',
                 flex: 0.68,
                 title: 'Tree',
                 displayField: 'DataName',
                 rootVisible: false,
                 useArrows: true,
                 hidden: true,
                 store: 'myStore'

This tree is a check tree (shows checkbox). I looked into following example of XML tree:

http://docs.sencha.com/extjs/4.1.1/#!/example/tree/xml-tree.html

When you expand the node of this tree, it shows loading icon.

I want to do something similar within my tree panel but I am not able to do so in my tree. Please help