After a period of trimming stakes, Warren Buffett's Berkshire Hathaway ended the year making some sizable insider purchases. Building one of those stakes continued into the new year. Meanwhile, other insiders returned to add to stakes as well in a telecom and a boat maker.

Another recent buy for Berkshire was an addition to its Sirius XM Holdings ( SIRI 1.18%) stake. Berkshire has been invested in Sirius' Liberty Media tracking stock since 2016, but increased its stake in Sirius after its simplification merger with the tracking stock this past September.

It's the Christmas season. Warren Buffett may not realize it, but he's the Santa Claus of investing. A lot of people watch what the icon owns, among the more than three dozen publicly traded stocks at Buffett's famous holding company.