Nuin, whose assigned tree is the ash tree (Fraxinus excelsior usually) has historically been placed as the fifth few of the Ogham, as can be seen in most ancient documents, but some have speculated that it was in fact the third few. The first three fews then become BLN, which has been linked to the Celtic sun-god Belenos, which may not be “academically correct”, but at least has interesting symbolism connected to it.
The ash tree is tall, seeing far of lands, other perspectives, allowing us to transcend our limited point of view and expanding it but connecting and communicating with other points of view. For this reason it has been connected to the World Tree (though the yew tree is also a fair candidate). If ever we feel stuck, within a certain situation or even our own psychology, the ash tree may help us break free with its spear-like strength and accuracy (its wood was, in fact, used for spears).
Keys are also significant in connection to ash; the unlock doors, allowing us to access other spaces, so that we can move around. But keys are also the name of the seeds peculiar to the ash. They have little “wings” allowing them to float far away from their parent tree, reaching low to the ground, connecting upper to lower, which then grow into tall trees, connecting lower with upper again. It is a tree for “thinking globally and acting locally”, finding the synthesis between the two perspectives.