Inserindo várias linhas na tabela - obtendo o erro ORA-00933:comando SQL não finalizado corretamente

Sintaxe errada.

Qualquer

insert into employee (employee_id, last_name, salary)
  values (129, 'khaj', 19000);
insert into employee (employee_id, last_name, salary)
  values (130, 'ravi', 20000);

insert into employee (employee_id, last_name, salary)
  select 129, 'khaj', 19000 from dual union all
  select 130, 'ravi', 20000 from dual;

ou mesmo

insert all
  into employee (employee_id, last_name, salary) values (129, 'khaj', 19000)
  into employee (employee_id, last_name, salary) values (130, 'ravi', 20000)
select * from dual;