There are many great extensions available for Visual Studio Team Services (former VSO), in the Market Place. One of them is Work Item Visualization Extension. You can add this extension to your Visual Studio Team Services (VSTS) account.
First browse the extension in market place.
Click on Install.
Select the VSTS account.
Confirm to install the extension.
Extension installed for the VSTS account. 
Work items can be visualize with the extension, with drill down capability.
