UnitedHealth Group stock has been rallying on news that Berkshire Hathaway has invested in the business. Warren Buffett is the CEO of Berkshire Hathaway and the investment could be seen as a possible vote of confidence in UnitedHealth's business.

While the "vote of confidence" from Buffett's investment validates the long-term value of UnitedHealth shares, the "management needs to regain trust and credibility with investors, and get back to its beat and raise reputation of the past," said James Harlow, senior vice president at Novare Capital Management.

Berkshire Hathaway's $1.6 billion stake in UnitedHealth Group is helping to lift the Dow Jones Industrial Average to a new record as investors pile into healthcare sector funds.