MediaAlpha, a three-year-old West Los Angeles company that provides a real-time ad bidding platform for the insurance industry, has received a majority investment from White Mountains Insurance Group in New Hampshire, the companies announced Tuesday. The amount of the investment and size of the stake were not disclosed.

Steven Yi, MediaAlpha’s chief executive, said the investment will allow the company to “redouble” its efforts in expanding its real-time online advertising exchange. The company currently works with about 40 ad buyers and roughly 25 publishers, including price comparison websites. Yi said he is particularly interested in bringing additional Web publishing partners into the fold.

Auto insurer Esurance, which White Mountains sold to Allstate 2011, is one MediaAlpha’s principal customers on the exchange, according to Yi.

Yi said he and his two co-founders were introduced to White Mountains by Esurance representatives.

MediaAlpha also has offices in Redmond, Wash.