New York (CNN Business) Bitcoin prices shot up 15% Tuesday and briefly rose above the $5,000 level for the first time since November. But good luck finding a reason to explain the sudden spike.

Nigel Green, founder and chief executive of deVere Group, simply said in a report that "there is a growing sense that Bitcoin is back."

Green added that "this dramatic jump is likely to attract many investors who have been sitting on the sidelines," including big institutions.

Wild swings for bitcoin are the norm. So this shouldn't be all that surprising, argued Naeem Aslam, chief market analyst with TF Global Markets (UK) Ltd, in a report.

"Bitcoin is a kind of a beast which has the ability to score more than 20% gain on a daily basis and we have seen this kind of rally towards the end of 2017 before the price crashed," Aslam wrote.

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