A trust created by an employer as a part of a stock bonus, pension, or profit-sharing plan for the exclusive benefit of some or all of his employees, to which contributions are made by the employer, or employees, or both, for the purpose of distributing to the employees the earnings and principal of the fund accumulated by the trust in accordance with such plan, shall not be taxable under R.S. 47:181, but the amount actually distributed or made available to any distributee shall be taxable to him the year in which so distributed or made available to the extent that it exceeds the amounts paid in by him.