One of the biggest bitcoin bulls on Wall Street says cryptocurrencies are in a massive bubble. He’s still starting a $500 million fund to invest in them. “This is a bubble and there is a lot of froth. This is going to be the biggest bubble of our lifetimes,” hedge fund manager Mike Novogratz said at a cryptocurrency conference Tuesday in New York. Novogratz, who’s says he began investing in bitcoin when it was at $90, is starting the crypto fund because of the potential for the technology to eventually transform financial markets.