No trustee shall directly or indirectly buy or sell any property for the trust from or to itself or an affiliate; or from or to a director, officer, or employee of such trustee or of an affiliate; or from or to himself, a relative, employer, partner, or other business associate; provided a national banking association or a state bank and trust company performing trust functions, where acting as executor, administrator, guardian, or trustee, may sell stock of itself to one or more of its officers, stockholders, or directors upon a court of competent jurisdiction finding that such sale will be for the best interest of the trust estate and making an order for such sale.