Scatter objects (and their children) with particle system in blender 2.8+

I’d like to create a particle system that scatters a bunch of trees. However I run into the following problem:

  1. I create my tree (with leaves) using the MTree Add-On.

  1. I create a particle system on my ground plane to scatter my trees.

As you can see, the particle system ignores my leaves since they’re sub-objects of my actual tree. How can I tell my particle system to display all objects in my collection including their children?