Citigroup (C - Get Report) didn't have the most mind-blowing second quarter from the i-banking space, but one under-the-radar big name in finance is long-term bullish the name.

"Citigroup...projected $9 a share of earnings for 2020," said Greenhaven Associates Wachenheim to TheStreet's Jim Cramer at the Delivering Alpha conference Wednesday. "But, if you increment it to the new tax rate, it's $10.20."

At its current stock price, Citigroup shares trade at a ridiculously cheap 6.8 times Wachenheim's 2020 profit estimate on a price-to-earnings multiple basis.  Wachenheim thinks Citigroup's stock is worth $130 relative to $70 currently.

Cramer is also bullish on Citigroup and the banks. 

"It's really hard to sell the banks [stocks] because they really are cheap," Cramer told TheStreet. Cramer added that Citigroup had an "excellent" second quarter earnings call. 

Citigroup Inc. (C - Get Report) shares fell on Jul. 13 due to concerns about slowing revenue growth in its North American credit-card business, even as the U.S. bank reported a jump in second-quarter profit thanks to the expected windfall from President Donald Trump's tax cuts.

Investors and analysts focused on troubling trends in the credit-card business, where revenue of $4.76 billion was flat compared with a year earlier, and down 4% from the first quarter. At the same time, interest income from Citi-branded credit cards in North America slipped to 8.28% of average loans, from 8.4% in the first quarter and 8.61% a year earlier. And losses on the credit-card loans jumped by 8%.

TheStreet's Bradley Keoun contributed to this story.

Citigroup is a holding in Jim Cramer's Action Alerts PLUS. Here's the research behind the call