I have rebuilded my taxonomy facets index, and the facets now show top hierarchical terms, and no more children terms, which are the terms used in the content. I don't know how to display the correct terms (probably missed something).
Basically I'd like to display both, as a choice offered to the user to catch the content with parents (previously thinked as categories in my context) or children terms (which are more specific). I thought it was possible to do so without having to use 2 vocabularies (and add both parent terms and children terms in the node). But maybe I'm wrong.
Thank you for answering.