BPS variable type EXIT to expand hierarchy

Hello,

Any idea how I can get all elements under a particular node (chosen by the user through a variable) of a hierarchy using a Function module in BPS?

I have been trying to do this using Function 'RSSH_HIERARCHY_READ' with the following code and parameters (see below)

Could anyone tell me how to proceed next?

Thanks in advance

Points will be assigned

*"----

""Local Interface:

*" IMPORTING

*" REFERENCE(I_TYPE) TYPE UPC_Y_VAR_TYPE

*" REFERENCE(I_AREA) TYPE UPC_Y_AREA

*" REFERENCE(I_VARIABLE) TYPE UPC_Y_VARIABLE

*" REFERENCE(IS_HIE_KEY) TYPE UPC_YS_HIE_KEY

*" EXPORTING

*" REFERENCE(ET_HIE_NODES) TYPE UPC_YT_HIESEL

*"----

DATA: BEGIN OF wa_val,

from TYPE rsleaffrom,

to TYPE rsleafto,

END OF wa_val,

wa_hierdir TYPE rshi_s_hiedir,

wa_hiedirkey TYPE rshi_s_rshiedirkey,

wt LIKE wa_hiedirkey OCCURS 0 WITH HEADER LINE,

ls_hie_nodes TYPE upc_ys_hiesel,

tb_node_val TYPE rshi_t_hienode,

tt LIKE LINE OF tb_node_val,

tb_interval TYPE rshi_th_interval.

SELECT SINGLE hieid objvers FROM /bic/hystopid

INTO wa_hiedirkey

WHERE nodename = '00001'.

CALL FUNCTION 'RSSH_HIERARCHY_READ'

EXPORTING

i_rshiedirkey = wa_hiedirkey

i_date = sy-datum

IMPORTING

e_rshiedir = wa_hierdir

e_t_rsnodes = tb_node_val

e_th_rsinterval = tb_interval

EXCEPTIONS

invalid_hierarchy = 1

name_error = 2

iobj_not_found = 3

OTHERS = 4.