Stanford parse tree - What does SBAR mean?

Question

I am wondering what SBAR means and how do I correctly represent in a tree this sentence? Why there are 2 S? Original sentence is: After she ate the cake, Emma visited Tony in his room. Thank you!

(ROOT
  (S
    (SBAR (IN After)
      (S
        (NP (PRP she))
        (VP (VBD ate)
          (NP (DT the) (NN cake)))))
    (, ,)
    (NP (NNP Emma))
    (VP (VBD visited)
      (NP
        (NP (NNP Tony))
        (PP (IN in)
          (NP (PRP$ his) (NN room)))))
    (. .)))

Answer 1

(I guess the answer goes here, not the comments; oops.)

According to this reference (http://bulba.sdsu.edu/jeanette/thesis/PennTags.html), SBAR is "SBAR - Clause introduced by a (possibly empty) subordinating conjunction." In this case, that conjunction is 'after'.

There are two S because 'she ate the cake' is an S, embedded within the larger S via the SBAR structure (using 'after').