The second major security based on bitcoin is starting to trade on the Chicago Mercantile Exchange.\r\nThe CME Group, one of the nation\u2019s largest exchanges of options and futures in the US, opened up bitcoin futures for trading at 6 p.m. EST Sunday. The initial price for bitcoin futures was $20,650, and the digital currency was trading at $20,135 at 6:08 p.m. EST.\r\nThe digital currency has exploded in popularity and value this year while drawing concerns about its volatility.\r\nThe CME bitcoin futures, like the bitcoin futures that now trade on the Chicago Board Options Exchange, do not involve actual bitcoin. They will track an index of bitcoin price. Each contract will be for 5 bitcoin. The CBOE started trading its own bitcoin futures on December 10.