Greentree played three seasons at the NCAA level, posting 101 points (41 goals, 60 assists) in 79 total games for the University of Alaska-Fairbanks. He appeared in eight games down the stretch for the Phantoms during the 2006-07 season, recording the first two goals of his pro career in the process.
Signed a two-way contract as a free agent with the Philadelphia Flyers at the conclusion of his collegiate career in 2007.
2006-07: The wingers third, and final, season with the University of Alaska-Fairbanks (CCHA) resulted in career-high numbers for Greentree: 21 goals and as many assists through 39 games. He also tallied 78 penalty minutes, a personal best with the club. In eight games with the Philadelphia Phantoms (AHL), his first look at professional hockey, he recorded two goals.
2007-08: This season marked his second with the Philadelphia Phantoms (AHL), and the winger put up some respectable numbers. In 72 games with the club, Greentree recorded 24 assists and netted 24 goals, totaling 48 points during the regular season. He saw ice time with the Flyers as well, appearing in two games during their regular season. In postseason action back with the Phantoms, he appeared in 12 games, recording another three assists and a goal. Traded to Calgary from Philadelphia for Tim Ramholt in 2008.
2008-09: In his first season with Quad City (AHL) after a trade from Philly, Greentree tallied a career-high 39 goals and 76 points in his second full season in the pros. He also suited up for two games with Calgary, but failed to register any points in his first look at the NHL with the Flames.
2009-10: Dealt to Chicago Blackhawks from the Calgary Flames.