Why does only one file work when creating a "portable" site menu on django-sitetree?

Question

Django

The manual https://django-sitetree.readthedocs.io/en/latest/a... tells how to do it.
But I have several applications in the project, I added sitetrees.py to each (all have the same menu name), but when executing
python manage.py sitetree_resync_apps
is added to the menu from only one file, everything else is deleted, even what was added to base manually.
How can I add items from all applications?