A trust created by an agreement between a group of the stockholders of a corporation and the trustee or by a group of identical agreements between individual stockholders and a common trustee, whereby it is provided that for a term of years, or for a period contingent upon a certain event, or until the agreement is terminated, control over the stock owned by such stockholders, either for certain purposes or for all purposes, is to be lodged in the trustee, either with or without a reservation to the owners, or persons designated by them, of the power to direct how such control shall be used