(a) The district may provide for a retirement system; provided, that the adoption, terms, and conditions of any retirement system covering employees of the district represented by a labor organization in accordance with this section shall be pursuant to a collective bargaining agreement between such labor organization and the district.
(b) If the district establishes a retirement board for the retirement system, board members and employees of the district may serve on the retirement board.
(c) The district may establish trust accounts for the purposes of this section.