Actually, there is something you can do that maybe can be useful for your purpose:
If you have the original tree, you can share it online, right?
Doing so your parent can modify the tree (with also images).
But you, in the meantime, can keep working on your original tree, because when your parent has finished his contribution, you can reimport his tree (it is a zipped JSON) in your original tree WITHOUT LOSING ANY CHANGES YOU MADE IN THE MEANTIME.
It's not the same, but maybe can be helpful to know that.
take care,
Yuri