A group of 12 U.S. Bitcoin exchange-traded funds have drawn strong inflows, with investors pouring in about US$4.2 billion so far in May. In options markets, traders built eye-catching Bitcoin positions earlier this week with the US$110,000, US$120,000 and US$300,000 calls expiring on June 27 logging the most open interest — or number of outstanding contracts — on Deribit, the derivatives exchange.