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

Warren Buffett’s net worth makes him 28 times richer than Donald Trump thanks to decades of savvy investing and Berkshire Hathaway's growth.

What Happened: The undisclosed investments of Berkshire Hathaway have been made public. The company has reportedly invested in steelmaker Nucor NUE +1.07% Get Free Report , homebuilders D.R. Horton DHI +1.30% Get Free Report and Lennar LEN +1.56% Get Free Report , with the total investments amounting to $1.8 billion.

In May, a 13F filing revealed that Berkshire Hathaway was buying mystery stocks. Now, at last, we know what they are.

No one can know, but here’s how to think about it.

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

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.

The investment comes as UnitedHealth faces soaring medical costs, federal investigations, the fallout of the killing of a top executive and a cyberattack last year.

Shares of UnitedHealth Group surged nearly 14% on Friday after billionaire Warren Buffett's Berkshire Hathaway bought 5 million shares of the company, providing a shot in the arm for investors who think the health conglomerate will turn around under its new CEO.

Leveraged positions in the stock market jumped 18% in one month and topped $1 trillion for the first time. Increasing use of debt to invest can tell us a lot about investors' attitudes. And while this has always been the case,