pixel_player29529770 When you come out on that large second floor, head to the right following the roses on the floor. It's not far.
With all of the earlier Events there is always some clue where to find the Treasure piece. In this case if you went straight up instead of to the right, then you would come upon a signpost with a picture of the Treasure on it and roses on the floor in front of it. That's telling you the roses will lead to the Treasure.