Inserting categories as a hierarchical terms from frontend form

Question

Use wp_set_object_terms( $object_id, $terms, $taxonomy, $append ); to get this done.

You are adding everything with add_post_meta which will not add category to your post type.

    wp_set_object_terms( $post_id, sanitize_text_field($_POST['some_field'] ), 'schooltype', true );

But here I am also not sure how to assign parent-children relationship via

wp_set_object_terms, even it’s not mentioned on WordPress codex! I think you should use:

wp_insert_term( $term, $taxonomy, $args = array() ); .

You can also check these links: