 HAMILTON, Bermuda, March 16, 2021 PRNewswire -- White Mountains Insurance Group, Ltd. NYSE: WTM announced today that MediaAlpha, Inc. MediaAlpha has filed a registration statement on Form S-1 with the Securities and Exchange Commission SEC for a proposed secondary offering of up to 7,000,000 shares not including shares subject to the underwriters option to purchase additional shares of its Class A common stock by certain selling stockholders. 