このコードの通知からアクティビティを起動するにはどうしたらいいでしょうか？

Question

MainActivity

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import com.example.testnotificationmanagerrepeat.R;

import java.util.Calendar;

public class MainActivity extends AppCompatActivity {

    private AlarmManager am;
    private PendingIntent pending;
    private int requestCode = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button buttonStart = this.findViewById(R.id.button1);
        buttonStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Calendar calendar = Calendar.getInstance();
                calendar.setTimeInMillis(System.currentTimeMillis());
                // 10sec
                calendar.add(Calendar.SECOND, 10);

                Intent intent = new Intent(getApplicationContext(), AlarmNotification2.class);
                intent.putExtra("RequestCode",requestCode);
                pending = PendingIntent.getBroadcast(
                        getApplicationContext(),requestCode, intent, 0);

                // アラームをセットする
                am = (AlarmManager) getSystemService(ALARM_SERVICE);

                if (am != null) {
                    am.setExact(AlarmManager.RTC_WAKEUP,
                            calendar.getTimeInMillis(), pending);            
             }
            }
        });
    }
}

AlarmNotification2

import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.WallpaperInfo;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.media.RingtoneManager;
import android.net.Uri;
import android.util.Log;

import com.example.testnotificationmanagerrepeat.R;

import java.text.SimpleDateFormat;
import java.util.Locale;

public class AlarmNotification2 extends BroadcastReceiver {

    private WallpaperInfo getApplicationContext;

    @Override   // データを受信した
    public void onReceive(Context context, Intent intent) {

        Log.d("AlarmBroadcastReceiver","onReceive() pid=" + android.os.Process.myPid());

        int requestCode = intent.getIntExtra("RequestCode",0);

        PendingIntent pendingIntent =
                PendingIntent.getActivity(context, requestCode, intent, PendingIntent.FLAG_UPDATE_CURRENT);
        String channelId = "default";
        // app name
        String title = context.getString(R.string.abc);

        long currentTime = System.currentTimeMillis();
        SimpleDateFormat dataFormat =
                new SimpleDateFormat("HH:mm:ss", Locale.JAPAN);
        String cTime = dataFormat.format(currentTime);

        // メッセージ　+ 11:22:331
        String message = "あくしろごみ "+cTime ;

        NotificationManager notificationManager =
                (NotificationManager)context.getSystemService(Context.NOTIFICATION_SERVICE);

        Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);

        // Notification　Channel 設定
        NotificationChannel channel = new NotificationChannel(
                channelId, title , NotificationManager.IMPORTANCE_DEFAULT);
        channel.setDescription(message);
        channel.enableVibration(true);
        channel.canShowBadge();
        channel.enableLights(true);
        channel.setLightColor(Color.BLUE);
        // the channel appears on the lockscreen
        channel.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
        channel.setSound(defaultSoundUri, null);
        channel.setShowBadge(true);

        if(notificationManager != null){
            notificationManager.createNotificationChannel(channel);

            Notification notification = new Notification.Builder(context, channelId)
                    .setContentTitle(title)
                    // android標準アイコンから
                    .setSmallIcon(R.drawable.mamedennkyuu)
                    .setContentText(message)
                    .setAutoCancel(true)
                    .setContentIntent(pendingIntent)
                    .setWhen(System.currentTimeMillis())
                    .build();

            // 通知
            notificationManager.notify(R.string.app_name, notification);

        }
    }