Quarterly filed Form 13Fs provide a way for investors to track the buying and selling activity of Wall Street's top money managers. Warren Buffett is occasionally granted the "confidential treatment" tag,

Berkshire Hathaway has built up sizable investments in a handful of companies, according to a filing released on Thursday.

Shares of some of UnitedHealth’s peers got a bump in the wake of Berkshire’s investment in the healthcare giant, and they all look cheaper based on price relative to expected earnings.