American investors might not be too familiar with Nu Holdings (NU -1.34%). True, it's a large-cap company with a $65 billion market capitalization currently. And yes, Warren Buffett's Berkshire Hathaway owned a stake in it for about three years. But because it operates in Latin America, Nu probably flies under the radar for many here in the U.S.This fintech stock has soared by an impressive 230% in the past three years (as of June 25), although it has taken investors on a volatile ride along the way. But sh ...