The pong pong tree—also known as the “suicide tree”—may be a plot point in the season finale of the HBO series. But the plant was known to cause thousands of deaths a year in the past.

Artist Sam Van Aken grew up on his family’s farm in Douglassville, Pa. As a result, his favored medium to create art is a process called tree grafting. It involves taking a scion, or a desired piece ...