Alphabet is the best-performing Magnificent Seven stock so far this year. Samuel Boivin / NurPhoto via Getty Images Close Key Takeaways Warren Buffett's Berkshire Hathaway has placed a big bet on one of the tech's hottest stocks. Berkshire (BRK.A)(BRK.B) purchased 17.8 million shares of Alphabet's Class A stock (GOOGL) in the third quarter, according to a regulatory filing made public earlier this month. A stake of that size in the Google parent would be worth nearly $5.7 billion as of Monday's close. Alph ...