SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 1)
    Function isConstant (children 1)
     ExpressionList (children 1)
      Function equals (children 1)
       ExpressionList (children 2)
        Literal \'a\'
        Literal \'b\'