The digital currency launched on the CBOE futures exchange in Chicago at 23:00 GMT Sunday, allowing investors to bet on whether Bitcoin prices will rise or fall. Its value had surged in the run-up to its futures debut, which saw it rise another 17% to above $18,000. Bitcoin's introduction to the CBOE has been seen by some as a step towards legitimising the currency. The move is expected to be followed next week by a listing on the rival Chicago Mercantile Exchange.