Starbucks shares jumped by as much as 5% Tuesday on news that the hedge-fund billionaire Bill Ackman had bought a stake in the coffee retailer. According to CNBC's Leslie Picker, Ackman disclosed the stake while presenting at the Grant's Fall 2018 Conference in New York. He had previously announced a position worth about $800 million, or 10% of his hedge fund's portfolio, in an undisclosed company in August. Pershing Square, Ackman's hedge fund, owns 15.2 million shares of Starbucks worth $900 million, according to CNBC. The stock has gained 1.5% this year.