A set of low polygon-count trees.  One with leaves, and one without.  They were created in Blender 2.81 and have been carefully modeled in order to produce the best product without adding unnecessary render time.

When people look at a 3D scene, the thing that pops out to them the most is "unnatural" looking nature.  If it's supposed to look real, it aught to react to light in a realistic way.  Some of the best looking models are low poly, but have great materials that react to light in a "natural" kind of way.