Izzie is wearing the sweater she knitted for Denny.
Mark Sloan (Eric Dane) makes his entrance by coming out of bathroom after a shower dawning only a towel and surrounded by steam. This is definitely a reminder to the audience that his nickname is "McSteamy."
Every episode of the show is named after a famous song. "I Am a Tree" is a song written by Doug Gillard.
This episode features a subplot in which Dr. Izzie Stevens bakes a large amount of muffins to deal with her grief. Guest star Chris O'Donnell's first film role was in the movie Men Don't Leave (1990) in which his mother, played by Jessica Lange, spends much of the movie baking muffins to deal with her grief.