expandable2.kt

 val icon = BitmapFactory.decodeResource(
                this.resources,
                R.drawable.ic_launcher_foreground
            )

            val not = NotificationCompat.Builder(this, "first")
                .setSmallIcon(R.drawable.ic_launcher_foreground)
                .setContentTitle("Hello There")
                .setContentText("General Kenobi!")
                .setLargeIcon(icon)
                .setStyle(
                    NotificationCompat.BigPictureStyle()
                        .bigPicture(icon)
                        .bigLargeIcon(null)
                )
                .setPriority(NotificationCompat.PRIORITY_DEFAULT).build()

nm.notify(5, not)