InsertQuery   (children 2)
 Identifier test_table
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 1)
    ExpressionList (children 4)
     Literal UInt64_1
     Literal NULL
     Literal \'\'
     Function tuple (alias x) (children 1)
      ExpressionList (children 1)
       Function toNullable (children 1)
        ExpressionList (children 1)
         Literal \'xxx\'
