Banking institutions may not have common directors unless the Commissioner finds that a common directorship is in the public interest and not detrimental to either banking institution. An individual who now is a director of more than one banking institution may complete the term of office of each directorship and may be reelected to each directorship. This section does not prohibit any person from being an officer, employee, director, or trustee of a mutual holding company and its subsidiary savings bank, shares of which are owned by the same mutual holding company.