I have multi-website, multi-store magento app. each store have different root category.
I have created user [sub admin] for each store and restricted access to their related store.
![enter image description here][1]


  [1]: https://i.sstatic.net/gGJlH.png

In each subadmin panel product grid i have to display his product only.
So I want to filter each product before display in grid, To do this i need the rootcategory id of current logged in subadmin store and each product rootcategory..
But whenever i try to get current subadmin store root category, Value is zero.
How can i solve this any suggestion,
If my idea is good... Then 

 1. How can I get currently logged in subadmin store's rootcategory?
 2. How can I get each product rootcategory?

Thanks in Advance..