Turns out trees are blessedly easy to make in Unity, so for once the assignment went swimmingly. Well, the second time: the first time materials were bugging out and we downloaded three different tree packs from the Asset store and they didn’t come with the properly-designed textures.
Unity literally comes with ‘tree’ as an available 3D object, and when you add it you can just start fiddling with its settings to make trees. Though I did keep getting this crash when trying to add textures to leaves, but I got around it by creating my own texture and applying an alpha channel.