LetExp([
 VarDec(x,true,NONE,
  IntExp(5))],
 SeqExp[
  LetExp([
   VarDec(y,true,NONE,
    IntExp(6))],
   OpExp(PlusOp,
    VarExp(
     SimpleVar(x)),
    VarExp(
     SimpleVar(y)))),
  VarExp(
   SimpleVar(x))])