Here’s a picture where you can see the tree hole it was in.
From the Wikipedia:
Dryad's saddle is an annual mushroom commonly found attached to dead logs and stumps or on living hardwood trees at one point with a thick stem. Generally, the fruit body is round and between 8–30 centimetres (3–12 inches) acros – exceptionally 60 cm (24 in) – and up to 10 cm (4 in) thick. The body can be yellow to brown and has "squamules" or scales on its upper side. On the underside one can see the pores that are characteristic of the genus Cerioporus; they are made up of tubes packed together closely.
It was high up so I couldn’t see the "squamules".