The thread you link to works with Omeka 2.x, so following what’s there and watching for where the other threads refer to Omeka 2 should do the trick. There’s nothing new that would break the solutions found in those threads.
One more question related to collection tree, how can we remove those bullets from collection tree public view? I intend to use a numbered list in collection tree.
Quickest, simplest option is probably to look in views/helpers/CollectionTreeList.php and views/helpers/CollectionTreeFullList.php for the <ul> tags and change them to <ol>