TheStreet. Warren Buffett is arguably the most successful investor of all time. He's amassed an amazingly massive net worth by buying and usually holding stocks for the long haul. Trained under legendary value fund investor Benjamin Graham,

Warren Buffett's Berkshire Hathaway built a $1.6 billion stake in UnitedHealth last quarter, marking one of its last wagers with the investor as CEO.

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

Warren Buffett’s Berkshire Hathaway resumed selling shares of Apple in the second quarter, offloading a stake worth more than $4bn as the billionaire investor continued to cut one of his most profitable trades.

Warren Buffett's top 10 stock holdings in the Berkshire Hathaway portfolio shows a preference to several sectors.

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.

The most significant addition was UnitedHealth Group Inc (NYSE:UNH), with 5,039,564 shares, accounting for 0.61% of the portfolio and a total value of $1.572 billion. The second largest addition to the portfolio was Lamar Advertising Co (NASDAQ:LAMR),

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

Berkshire also revealed it has bought the common stocks of security products provider Allegion ( ALLE-N ), home builder DR Horton ( DHI-N ), outdoor advertiser Lamar Advertising ( LAMR-Q) and steel maker Nucor ( NUE-N ), and significantly increased its stake in homebuilder Lennar ( LEN-N ).

The Oracle of Omaha sent two-thirds of his company's largest investment holding packing in favor of a 7.7% stake in a steadily growing, consumer-facing business.