According to CoinDesk, the Chicago Mercantile Exchange (CME) has become the second-largest bitcoin futures exchange, with a notional open interest of $3.54 billion. This rise in open interest is reminiscent of the early stages of the 2020-21 bull run. CME has climbed from the fourth position seen weeks ago, while Binance, an offshore unregulated exchange, maintains the top spot with an open interest of $3.83 billion, 8% higher than CME.Open interest in CME's cash-settled futures contracts recently surpassed the 100,000 BTC mark for the first time on record. The exchange's share in the BTC futures market also rose to a new lifetime high of 25%. CME offers standard bitcoin futures contracts equivalent to 5 BTC and micro contracts sized at one-tenth of 1 BTC. Most open interest in offshore exchanges is concentrated in perpetual futures rather than traditional futures contracts.Some observers believe CME's ascent is a sign of an institutional-led rally, as bitcoin has risen 27% this month amid macroeconomic uncertainty and spot ETF optimism. Retail investors also seem to have played a part, with the rolling five-day volume in ProShares' industry-leading bitcoin futures ETF jumping by 420% to $340 million last week. However, André Dragosch, head of research at Deutsche Digital Assets, suggests that CME's rise results from the unwinding of bearish bets on offshore exchanges, rather than long futures positions being the main driver behind the recent surge.