In case you missed the Glee rendition of All By Myself, watch it below. You will be interested to know that the song actually borrows from Rachmaninoff's Piano Concerto No. 2 in C minor (movement 2). Why do I know this? I was playing Baby Max some classical music from an old album of my parents, and I recognized the tune. After some difficult Wikipedia searching (it came up immediately) I found the facts.