In an unprecedented investment journey spanning over 58 years, Warren Buffett's transformational leadership at Berkshire Hathaway has produced a stunning cumulative return of over 3,200,000% and a compound annual growth rate of 19.4%. While much of this growth is credit to vital moves in the insurance industry, Buffett's latest buying spree discloses a sudden focus on Berkshire Hathaway itself.

According to the latest reports, Apple leads Berkshire's portfolio, amounting nearly half of its total value. Despite occasional sales for tax purposes, Buffett persistently adds to Berkshire's Apple position, disclosing his resolute confidence in the tech giant. Yet, there's another stock Buffett has been silently accumulating more than any other in the past five years, a stock that doesn't appear on form 13F – Berkshire Hathaway itself.