Datagrid - How can I get the row number of parent row in a hierarchical grid.

I have created a collection of my class This collection has a hierarchy of the order Batch -> Documents -> Properties This is not a Dataset but a user defined collection. I have bound this collection to a Datagrid. Now when I am viewing the Properties for a Document under a Batch, how can I find the row number to which this document belongs? as the currentcell property returns the row/column of the current cell (Properties) & the CurrentRowIndex returns the row number of the Batch selected.