dropdown button not properly scaled with tall item

dropdown_button.dart

// Flutter code sample for

// This sample shows a `DropdownButton` with a customized icon, text style,
// and underline and whose value is one of "One", "Two", "Free", or "Four".
//
// ![A screenshot of the dropdown button](https://flutter.github.io/assets-for-api-docs/assets/material/dropdown_button.png)

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

/// This Widget is the main application widget.
class MyApp extends StatelessWidget {
  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: MyStatefulWidget(),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  MyStatefulWidget({Key key}) : super(key: key);

  @override
  _MyStatefulWidgetState createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  String dropdownValue = 'One';
  List<String> items = <String>['One', 'Two', 'A repeating, long selection. A repeating, long selection. A repeating, long selection. A repeating, long selection. A repeating, long selection. A repeating, long selection. A repeating, long selection. A repeating, long selection. ', 'Four'];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        children: <Widget>[
          DropdownButton<String>(
            isExpanded: true,
            value: dropdownValue,
            icon: Icon(Icons.arrow_downward),
            iconSize: 24,
            elevation: 16,
            style: TextStyle(color: Colors.deepPurple),
            onChanged: (String newValue) {
              setState(() {
                dropdownValue = newValue;
              });
            },
            items: items.map<DropdownMenuItem<String>>((String value) {
              return DropdownMenuItem<String>(
                value: value,
                child: Text(value),
              );
            }).toList(),
          ),
        ],
      ),
    );
  }
}