Hi Naveen,
To get RooT data you have to use to_root association as in your case root is also a parent node you can use to_parent association also.
io_read->retrieve_by_assocation
exporting
it_key = lt_key " key table that hold item keys
association = item-to_root " association name (it is created by default)
fill_data = abap_true " make it to fetch data
Importing
et_data = lt_root_data
you will get your root data in lt_root_data.
Regards
LK