Buffett invested in Heinz in 2013 and two years later, Heinz merged with Kraft Foods. He bought 326 million shares during this merger at a cost of around $24.6 billion. He has held on to that stake, which is now worth $11.4 billion.

Warren Buffett-led Berkshire Hathaway's (NYSE: BRK.A)(NYSE: BRK.B) had a substantial investment in General Motors (NYSE: GM). According to Berkshire's SEC filings, the conglomerate owned 50 million shares of GM at the beginning of that year,

The Oracle of Omaha's secret portfolio contains 120 securities -- one of which is a historically cheap AI stock.