Multiple images/pictures in onActivityResult

Question

I have 2 buttons:

1. on 1 button I can take pictures
2. on the other button I can select pictures from the gallery.

The problem is when I take a picture it is displaying it, but when I take a another picture it is replacing the current picture, but what I want is that the pictures comes underneath each other. So for example I select 1 picture from the gallery and I take 2 pictures, I want to see 3 pictures but I can't find the right solution to it.

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Button btnCamera = findViewById(R.id.btnCamera);
    imageView = (ImageView)findViewById(R.id.imageView);
    btnTakeImg = (Button)findViewById(R.id.btnTakeImg);

    // Open camera and take picture
    btnCamera.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
            startActivityForResult(intent, 0);
        }
    });

    // Pick image from gallery
    btnTakeImg.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            openGallery();
        }
    });
}

private void openGallery() {
    Intent gallery = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.INTERNAL_CONTENT_URI);
    startActivityForResult(gallery, PICK_IMAGE);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if(resultCode == RESULT_OK && requestCode == PICK_IMAGE) {
        imageUri = data.getData();
        imageView.setImageURI(imageUri);
    }
    if(resultCode == RESULT_OK && requestCode == 0) {
        Bitmap bitmap = (Bitmap)data.getExtras().get("data");
        imageView.setImageBitmap(bitmap);
    }
}