[FOLIAGE] ~ Trees: single atlas with opacity mask, or two separate materials for trunk and leafs?

The question is simple: what should I favour, draw calls or shader complexity?

In foliage, leafs and smaller branches are flat planes with an opacity mask, which reduces polygons drastically, but also makes the shader heavy because of the transparency check.
Usually I apply two separate materials one for the trunk and one for the leafs, but recently I’ve started using atlases, which made me re-evaluate the method I use to texture trees and larger bushes.

What would be better?
Reducing draw calls by applying a single atlas/material to the whole tree, which would require a transparency check for the whole model…
using two distinct materials, one for the trunk and one for the leafs to reduce the transparency check?

two distinct materials