вы можете использовать пользовательский вид, подобный этому
создать уведомление_view.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="64dp"
android:padding="10dp" >
<ImageView
android:src="@mipmap/ic_launcher"
android:id="@+id/icon"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:layout_alignParentLeft="true"
android:layout_marginRight="10dp" />
<TextView
android:textSize="13dp"
android:textColor="#000"
android:text="Testing"
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="@id/icon"
/>
<TextView
android:textSize="13dp"
android:textColor="#000"
android:text="Testing is awecome"
android:id="@+id/desc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="@id/icon"
android:layout_below="@id/title"
/>
</RelativeLayout>
и в коде
RemoteViews customview = new RemoteViews(getPackageName(), R.layout.custom_push);
customview.setImageViewResource(R.id.icon, R.mipmap.ic_launcher);
customview.setTextViewText(R.id.title, "Notification title");
customview.setTextViewText(R.id.dex, "Notification Description");
NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this).setSmallIcon(R.drawable.icon).setContent(customview);
Notification notification = mBuilder.build();
notificationManager.notify(NOTIFICATION_ID, notification);