A mutual savings bank may invest its funds in the purchase of United States government securities from a bank or trust company, subject to the selling bank's or trust company's agreement to repurchase such securities on the business day next following their purchase by the mutual savings bank. The securities may be purchased at par, or at a premium or discount, as the mutual savings bank may agree, and may be characterized for accounting and statement purposes and carried on the books of the mutual savings bank as such securities to the extent of their market value, and as due from such banks or trust companies to the extent that the repurchase price agreed to be paid exceeds such market value.