How to Add Multiple Markers on Google Map in Flutter?

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'GFG',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      // First Screen of our App
      home: const HomePage(),
    );
  }
}

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

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

class _HomePageState extends State<HomePage> {

  // on below line we are initializing our controller for google maps. 
  Completer<GoogleMapController> _controller = Completer();

  // on below line we are specifying our camera position
  static final CameraPosition _kGoogle = const CameraPosition(
      target: LatLng(37.42796133580664, -122.885749655962),
    zoom: 14.4746,
  );

  // on below line we have created list of markers
  List<Marker> _marker = [];
  final List<Marker> _list = const [
    // List of Markers Added on Google Map
    Marker(
        markerId: MarkerId('1'),
      position: LatLng(20.42796133580664, 80.885749655962),
      infoWindow: InfoWindow(
        title: 'My Position',
      )
    ),

    Marker(
        markerId: MarkerId('2'),
        position: LatLng(25.42796133580664, 80.885749655962),
        infoWindow: InfoWindow(
          title: 'Location 1',
        )
    ),

    Marker(
        markerId: MarkerId('3'),
        position: LatLng(20.42796133580664, 73.885749655962),
        infoWindow: InfoWindow(
          title: 'Location 2',
        )
    ),
  ];

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _marker.addAll(_list);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Color(0xFF0F9D58),
        title: Text("GFG"),
      ),
      body: Container(
        // on below line creating google maps. 
        child: GoogleMap(
          // on below line setting camera position 
            initialCameraPosition: _kGoogle,
          // on below line specifying map type. 
          mapType: MapType.normal,
          // on below line setting user location enabled.
          myLocationEnabled: true,
          // on below line setting compass enabled. 
          compassEnabled: true,
          // on below line specifying controller on map complete. 
          onMapCreated: (GoogleMapController controller){
              _controller.complete(controller);
          },
        ),
      )
    );
  }
}