Section 8. Notwithstanding section 4, funds held in the trust department of any bank awaiting investment or distribution may be deposited in its banking department if such bank shall first transfer to its trust department, to be held as security therefor, bonds, notes, bills and certificates of indebtedness of the United States, of the commonwealth, or of any of the states or any other securities in which the bank may legally invest, of an aggregate value of not less an amount than funds so deposited, and such bank shall at all times maintain the value of such security at such amount; provided, however, that such security shall not be required to the extent that the funds so deposited are insured by the Federal Deposit Insurance Corporation.