Poet Tree

     AI
    POE
    GRAY
   DANTE
   HORACE
  KHAYYAM
  KALIDASA
 SOPHOCLES
 BAUDELAIRE
 SHAKESPEARE
     LI
     TU
     SU
ARISTOPHANES

Q. What is this curious list I see?
A. The answer is plainly, "Poet - tree".

-- Kay Haugaard, on the Word-A-Day mailing list