Wall Street thinks Upstart and Atlassian are undervalued ahead of 2026, and certain analysts are predicting big gains for shareholders.The S&P 500 (^GSPC +0.32%) has added 18% year to date amid excitement about the artificial intelligence boom. But not every AI stock has done well. Upstart Holdings (UPST 1.40%) and Atlassian (TEAM 0.78%) have declined 22% and 34%, respectively. But certain Wall Street analysts expect the stocks to rebound in a big way next year:Peter Christiansen at Citigroup has set Upstar ...