Interests in one or more common trust funds, as defined in and from time to time established, maintained and administered pursuant to the Common Trust Fund Act, the investments of which are not restricted to the investments otherwise authorized for representatives by Sections 21-1.01 through 21-1.04 and 21-1.06 of this Act, provided that the investment in such common trust fund meets the standard of the prudent person rule for the investment of trust funds; and provided further that in the case of an administrator, the approval of the court, by written order, be first obtained.