Adding data to a Hierarchical tree

i am having a tree with nodes as A-Z. i need to add data to these nodes from another table such that node A is having data as.. names of all the employees starting with alphabet 'A'..etc
i am using a procedure to retreive the data.
PROCEDURE proc_add_tree_data(str char) IS
BEGIN
 
 declare
  htree         ITEM;            
CURSOR cur_tree_query IS
   select distinct emp_first_name
         from emp_info_hdr
         where emp_first_name like str||'%';
         ename emp_info_hdr.emp_first_name%type;
        begin
              htree := Find_Item('BLOCK_TREE.HTREE');
              open cur_tree_query;
         LOOP
               fetch cur_tree_query into ename;
               Ftree.Add_Tree_Data(htree,
               Ftree.ROOT_NODE,
               Ftree.PARENT_OFFSET,
               Ftree.LAST_CHILD,
               Ftree.QUERY_TEXT,
               ename);
         
               exit when cur_tree_query%notfound;
         end loop;
         close cur_tree_query;
          
         END ;
 
END;

but this cursor is giving me error...invalid query for hierarchical tree.