Thank you very much for contacting me.
I tried the following.
It didn’t work.
[1] Added to functions.php
function registered_post_hierarchical ($ post_type, $ post_type_object) {
if ($ post_type ==’post’) {
$ post_type_object-> hierarchy = true;
add_post_type_support (‘post’,’page-attributes’);
}
}
add_action (‘registered_post_type’,’registered_post_hierarchical’, 10, 2);
[2] Use the menu generated in [1] to specify the parent post from the edit screen of the child post.
[3] Parent posts are members of the child category
[4] Breadcrumb NavXT settings
Post / Post hierarchy → Parent post