A Wall Street investment chief says the relentless surge in big tech stocks is headed for an abrupt ending — and warns it could sink the entire market by 40%

· Investors have bid up the largest technology stocks to valuations that are unsustainable and set to roll over, according to David Bahnsen, the founder and chief investment officer of The Bahnsen Group.
· In an interview with Business Insider, he shared his concerns about big tech besides stretched valuations, and explained...