Urn1 contains three white balls and one black ball, while Urn2 contains two white balls and five black balls. One ball is drawn at random from Urn1 and placed in Urn2. A ball is then drawn from Urn2. If the ball drawn from Urn2 is white, what is the probability that the transferred ball was white? Use a tree diagram to describe the setup.

I'm confused about how to set up this tree diagram. Please help.