I'm confused how two different people mixed the Forest Temple up with The Great Deku Tree
Anyways, glad you found the missing key. Peopls love to claim the Water Temple is confusing, but the Forest Temple is just as good at twisting you up and making you miss keys
Tip for upcoming water temple btw - The animation does not show it in the original game, but a platform at the bottom of the central tower floats up and reveals a hidden passage. This one spot trips up a TON of people