Right, first question before everyone piles in with drone explanations - what was the light behaviour like? Static hover, pulsing, rotating? That's the thing most people forget to note in the moment and it's the single most useful piece of information for ruling things out.
I've been chasing this stuff around Norfolk for better part of 25 years and the tree line sightings are their own particular category. Something about the boundary between open sky and tree canopy seems to be a genuine hotspot, not just for UAP but for the stranger stuff too. Had one myself near Holt back in 2019 that I still cant fully account for and I'm not someone who says that lightly.
Write down everything you remember right now before your brain starts filling in gaps. Date, time, duration, compass direction if you know it, weather conditions. People think they'll remember but they dont. Memory is a traitor.