Warren Buffett's Berkshire Hathaway Inc. BRK.A, +0.51% BRK.B, +0.15% started new stakes in Biogen Inc. BIIB, -0.37% and Kroger Co. KR, -1.40% while increasing its stake in Kraft Heinz Co. KR, -1.40%, the company disclosed late Friday in a Securities and Exchange Commission filing. Berkshire reported a stake of about 648,000 shares of Biogen and 549,000 shares of Kroger that were not listed in last quarter's filing. Kroger shares rose 6% after hours, while Biogen shares advanced 2%. Also, Berkshire increased its stake in Kraft to about 10.5 million shares from 9.1 million in the previous quarter. Berkshire cut its stake in Travelers Cos. TRV, +0.64% to about 312,000 shares from a previous stake of nearly 6 million shares.