Warren Buffett’s Berkshire Hathaway Inc. bought shares of UnitedHealth Group Inc. in the second quarter, sending the health insurer’s stock soaring in post-market trading.

The chief executive officer of the Omaha, Nebraska-based conglomerate acquired 5 million shares in UnitedHealth, granting Berkshire a stake worth $1.6 billion, according to a filing Thursday. Berkshire also sold its $1 billion stake in T-Mobile US Inc. during the period, exiting the telecommunications operator.