It's been a tough go of it for Bitcoin (CRYPTO: BTC) recently, which is down 16% for the year. According to the latest quarterly Securities and Exchange Commission (SEC) 13F filings, billionaire hedge fund manager Paul Tudor Jones nearly doubled his stake in the iShares Bitcoin Trust (NASDAQ: IBIT) from 4.4 million shares to 8.1 million shares. As of mid-February, he had 4.5% of his $9 billion portfolio invested in this spot Bitcoin exchange-traded fund (ETF).