The Oracle of Omaha has been socking hundreds of millions of dollars away in an investment that currently yields almost 4%.Warren Buffett will retire as CEO of Berkshire Hathaway (BRK.A 0.50%) (BRK.B 0.39%) at the end of 2025 and leave Greg Abel in charge. The $1 trillion conglomerate constructed by Buffett over the last 60 years operates a diverse array of wholly owned subsidiaries, and also owns a stock portfolio worth about$314 billion as of this writing.But just because Buffett's tenure as the head of ...