This is the most grueling bank on Wall Street where young bankers say they work 90 hours a week

REUTERS/Brendan McDermid

LionTree founder Aryeh Bourkoff

Investment banking is famous for imposing long hours on its young workers.

But one firm has hours that are really tough, even for banking.

It's boutique advisory firm LionTree Advisors, whose professionals worked on average 90 hours per week, according to a report by Wall Street Oasis, an online community for financial professionals.

Co-founded by former UBS media investment banker Aryeh B. Bourkoff in 2012, LionTree Advisors is well-known for working on high profile transactions that are reshaping the telecom, tech, and media landscape. This includes advising Charter on its attempt to by Time Warner Cable, Snap on its initial public offering, and Verizon on its acquisition of Internet pioneer AOL.

The firm is known for its culture of openness and a flat structure - few of its staff has formal job titles and young bankers are encouraged to bring up transaction ideas, according to a New York Times story.

A representative for LionTree Advisors did not respond to a request for comment.

So-called boutique bands tend to have more grueling hours than their bulge bracket counterparts, the report found. Young workers at tech and media boutique Allen & Company and healthcare focused firm MTS Health Partners work an average of 87.5 hours per week each, according to the report.

Big U.S. investment banks such as Goldman Sachs (73.6 hours) and JP Morgan Chase (69.1 hours) are relatively less intense and draining, among the 155 firms surveyed in the study.

Banks generally have put in measures to reduce the workload and stress of their junior staff, such as requiring Saturdays be taken off, following the death of a Bank of America intern in 2013.

But bankers still put in much longer hours than typical Americans who work an average of 34.5 hours per week, according to July data from the Bureau of Labor Statistics.