A bank may subscribe to, invest in, buy, or own voting stock of one or more bankers banks, foreign bankers banks, bank holding companies, or foreign bank holding companies of such bankers bank or foreign bankers bank in an amount not to exceed five percent of any class of voting stock of each such bankers bank, foreign bankers bank, bank holding company, or foreign bank holding company of such bankers bank or foreign bankers bank. In no event shall such bank’s holdings of the stock of a bankers bank, foreign bankers bank, bank holding company, or foreign bank holding company of such bankers bank or foreign bankers bank exceed ten percent of the capital stock and paid-in and unimpaired surplus of the bank holding such stock.