How to create huge amounts of 3D models

Hi everyone,
I am working on a project and the goal is to visualize huge amounts of trees (in four different categories) using Cesium.
From my understanding, I have to create a tileset (with .i3dm files from 3d models) for that? is this correct?
Is there a way to do this using Cesium ION? If yes, how? I’ve looked at several tutorials but did not find anything suitable! Is there a useful tutorial?

Thanks,