SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Literal UInt64_1 (alias a)
   ExpressionList (children 1)
    Subquery (children 1)
     SelectWithUnionQuery (children 1)
      ExpressionList (children 1)
       SelectQuery (children 1)
        ExpressionList (children 1)
         Identifier a