Berkshire Hathaway revealed four new investments Thursday in steelmaker Nucor, insurer UnitedHealth and two of the nation’s biggest homebuilders — Lennar and DR Horton — but only one of the investments was big enough to ensure that legendary investor Warren Buffett may have handled them.

Warren Buffett’s Berkshire Hathaway revealed a position in embattled healthcare giant UnitedHealth Group while showing smaller stakes in longtime holdings Apple and Bank of America, according to a regulatory filing Thursday.

Berkshire Hathaway’s portfolio added six new stocks, including the three new secret stocks. Warren Buffett was a net seller of stocks for the eleventh straight quarter.

The conglomerate sold Apple shares during the second quarter, though the iPhone maker remains Berkshire’s largest stockholding.

The Omaha-based conglomerate bought more than 5 million shares in the healthcare firm for a stake worth about $1.6 billion at the end of June.

Berkshire Hathaway ( BRK.A -0.05%) ( BRK.B 0.24%) is considered by many to be a reliable stock for long-term investors. It's outperformed the S&P 500 ever since a young Warren Buffett took over the company in 1965, and its evolution from an aging textile maker to a diversified conglomerate churned out millionaire-making gains.

Warren Buffett emphasizes that while achieving success is exciting, effectively correcting mistakes when they occur is equally critical for businesses.

Berkshire Hathaway’s $1 billion homebuilding investment indicates Warren Buffett’s confidence in a future U.S. housing market rebound.

Berkshire Hathaway recently filed its second-quarter 13F form, revealing its stock holdings at the end of June.