This example shows how to use Descendant function with Desc_Flag as self_before_after which means this will show all members at level - Subcategory_Category_Product. and to prove that we are getting correct result I am using Member Property - Level which shows Level Name to which Member Belongs

With
Member Measures.ProductStatus As [Product].[Status].Member_Key
Member Measures.Levela as [Product].[Product Categories].currentmember.level.name
SELECT descendants ([Product].[Product Categories].[Category].allmembers,[Product].[Product Categories].[Subcategory],self_before_after)
on 1 ,

http://blogs.msdn.com/b/karang/archive/2011/09/30/mdx-descendant-function-demo.aspx