create table emp1(
employee_id number,
employee_name varchar2(20),
Manager_id number);

insert into emp1
values (1, 'Elvin', 3);
insert into emp1
values (2, 'Tural', 3);
insert into emp1
values (3, 'Gulgun', 5);
insert into emp1
values (4, 'Ferid', 2);
insert into emp1
values (5, 'Orxan', null);

select * from emp1;