Categories in Hierarchical Order plugin maintains the hierarchical order of selected categories in the Category tab under your WordPress Admin Post Editor.
The selected category/categories to which a post belongs, are by default pushed at the top in the Category tab while saving the post. Whereas the plugin keeps the position of selected category/categories unchanged as per their parent/child relationship.
The plugin is available at the WordPress plugin repository along with further details. Additionally, you can also check our official website for the same. You are welcome to post issues, contribution and feature requests here.