Where a person who is a trustee of two or more trusts has mingled the funds of two or more trusts in the same aggregate of cash, or in the same bank or brokerage account or other investment, and a withdrawal is made therefrom by the trustee for his own benefit, or for the benefit of a third person not a beneficiary or creditor of one or more of the trusts, or for an unknown purpose, such a withdrawal shall be charged first to the amount of cash, credit, or other property of the trustee in the mingled fund, if any, and after the exhaustion of the trustee's cash, credit, or other property, then to the several trusts in proportion to their several interests in the cash, credit, or other property at the time of the withdrawal.