BOSTON (Reuters) - Billionaire investor William Ackman's hedge fund Pershing Square Capital Management has made a new bet on Warren Buffett's Berkshire Hathaway Inc , according to a regulatory filing made on Wednesday. This marks the first time that Ackman's $8 billion fund has announced a new position since late last year when it bought a stake in Starbucks Corp . The new stake will be a passive investment for Ackman's $8 billion firm, a person familiar with the matter said. Ackman bought 3.5 million of Berkshire's so-called B shares during the second quarter.