SQL & PL/SQL :: Stored Function In Where Condition

I use stored function in where condition but it gives wrong output but output of stored function is use in where condition it gives correct output. i don't know how to use it.

Scripts:

select get_emp_mgr_no('MHR,ERT,TYU') FROM DUAL;

OUTPUT:

'MHR','ERT','TYU'

SELECT count(1)
FROM BANK_details
where notre in ('MHR','ERT','TYU');

count:

12345

select count(1)
from bank_details
where notre in '('||get_emp_mgr_no('MHR,ERT,TYU')||')';

count

0

It shows wrong output. how to use stored function in where condition?