Hi :-) I guess you want to have exactly the same thing you talk on
https://forum.dokuwiki.org/post/59251 in Dokuwiki. I'm not an expert. For the subcategories there isn't any problem: you just have to create them and the result will be exactly what you want ;-) The problem is for the main page: For this you can use the start page on the root of your wiki, but it will be displayed at the end of the navigation bar instead of the beginning. If this can't be changed, perhaps you'll be force to create a main category just for this page :-D