How to select All child check box if we select root check box in file explorer?

Hi all,

I am using file explorer in my app.which is same as windows file Explorer by using below link :

http://gargmanoj.wordpress.com/2009/03/27/wpf-101-a-simple-windows-explorer-like-directory-browser/

In this file explorer i needed check box in front of each directory.So for that  i have added a check box control in  "HierarchicalDataTemplate"  so due to this check box is appearing in front of each directory which i needed.

but the issue is with selection of check box. Actually i want to fulfill two different conditions:

1. when i select any folder by check box it sub directory should automatically get select.

2. when i select sub directory its Root directory should automatically get select.

Please do needful.

Thanks 

sumitk