Seen similar over Swansea Bay a few years back. Just sat there, no sound, no movement for about 20 minutes then gone. No gradual fade, no flying off - just gone. Still bugs me.
The treeline detail is interesting though. A lot of these hovering sightings seem to hug the edge of woodland areas. Whether thats coincidence or not I dont know but its a pattern that keeps coming up, especially in bigfoot territory in the States which is its own rabbit hole entirely.
What colour was the light? And did it feel like it was watching you or just sort of... there? Sounds daft but theres a difference when you're standing outside in the dark looking at something that shouldnt be there. You know when something is aware of you.
Post a rough sketch if you can, even a phone drawing. Details matter on these early on before memory starts filling in gaps.