Eruvin 78: A Lion Crouches at the Entrance

A ladder that is dug out if the wall - handholds - must cover the whole height of the ladder. Which leads into the next case, that isn't quite a ladder: namely, a tree. Note that you wouldn't otherwise be able to climb the tree on Shabbat, but what about in its function as a means to ascend the wall? What about the tree as a place to put your eruv? It seems that at the end of the day, Shabbat overrides the possibility of using that tree as a passageway, which would be permanent over Shabbat (so it's not, and can't be used on Shabbat). Plus the case of the Asherah - is that not overkill? Or are they exploring all parameters, as we often expect?