It is possible to end up with duplicate entries in the document tree

Note: I identified the issue with file system but it might be more generic

reproduction steps

1. remove ~/.cristal
2. start an electron instance
3. edit and the main page
4. click on new page
5. set a name FirstSubPage
6. select the main page
7. click on create
8. edit the content and save
9. observe the document tree

Expected

A "root" page with a sub FirstSubPage item.

Actual

FirstSubPage is duplicated.