SelectWithUnionQuery (children 2)
 ExpressionList (children 1)
  SelectQuery (children 1)
   ExpressionList (children 2)
    Identifier x
    Subquery (alias x) (children 1)
     SelectWithUnionQuery (children 1)
      ExpressionList (children 1)
       SelectQuery (children 2)
        ExpressionList (children 1)
         Literal UInt64_1
        Literal NULL
 Identifier Null
