Work with me here. What if you lined a pair of customs with a plastic bag, mixed plaster of Paris and poured in to create trees?
Or some other substance? I’m thinking of expanding foam, but that stuff is a damn mess. Scratch that.
Some kind of art medium? How about the fiberglass wrap used for orthopaedic casts? A bunch of those rolls unwrapped, prepped and stuffed into the plastic bags and left to cure?