About $55 billion of Tesla Inc. shares were traded Tuesday as investors piled into a rally that has doubled the electric-car maker’s stock price since the start of the year.

To put it into context, that’s just over five times the volume of the stock with the day’s second highest turnover, Apple Inc. (AAPL).

As noted by analysts at Morgan Stanley, the record trading also exceeded this year’s average repo operation conducted by the Federal Reserve to support the overnight funding needs of the U.S. banking sector.

The average daily value of Tesla stock (TSLA) changing hands last year was $2.5 billion.

Touted reasons for the stock’s surge range from Chief Executive Officer Elon Musk delivering profit for the fourth time in six quarters to a simple short squeeze. Even so, Morgan Stanley’s Adam Jonas said that “many investors are struggling to identify a strong fundamental underpinning for the move.”

The brokerage doesn’t have the answers to investor queries on who is buying the stock, how high can it go or where there might be support, Jonas wrote in a report to clients Wednesday.

After closing at $887 Tuesday, the stock sits above his $650 bull case, Jonas added, reiterating his underweight rating. Tesla shares fell 4.5% to $847 a share in U.S. pre-market trading Wednesday.

“Folks are asking a lot of questions,” Jonas said.