shares of dollar tree inc rose 66 in premarket trade monday after the wall street journal reported that activist investor mantle ridge lp has taken a 18 billion stake in the discount retailer and is planning to push it to take moves to boost its stock price mantle ridge will push for changes at the companys family dollar chain the paper reported citing people familiar with the matter the investor is working with richard dreiling former ceo of dollar tree rival dollar general corp  who is credited with helping turn that company around in the early 2010s plans may include nominating directors to the dollar