Please Help Me To Make A Tree On Form

DECLARE
htree ITEM;
v_ignore NUMBER;
rg_emps RECORDGROUP;
BEGIN
htree := Find_Item('tree_block.htree3');
rg_emps := Create_Group_From_Query('rg_emps','select 1, level,first_name, NULL,employee_id'|| 
'from employees'||  
'connect by prior employee_id = manager_id'||  
'start with job_id = ''AD_PRES''');
v_ignore := populate_group(rg_emps);
ftree.set_tree_property(htree,ftree.record_group,rg_emps);
end;