The Adam tree is obviously a reference to the biblical Adam, but less talked about is how Ohara was an allusion to the Tree of Knowledge (of Good and Evil). Which makes sense, as the library housed all the secrets of the world, both good and bad. Water 7/Enies Lobby also marks our first real hint of devil fruit knowledge and Vegapunk will have his first name drop here in a chapter or two, so Oda's laying a lot of groundwork for future series lore. Later on in Fishman Island Oda will explicitly link the sunlight tree Eve with the treasure tree Adam, for those readers who might not catch the biblical allusions.
There's one more tree mentioned in the Genesis account of Adam and Eve, the Tree of Life, which was guarded by an angel with a flaming sword after they were kicked out of the Garden of Eden by falling to the tempted by the devil to eat the forbidden fruit.
It is interesting to me that the Adam tree is specifically found in a war-torn country when the Genesis account is so closely associated with the Garden of Eden, so it will be interesting to see what Oda does with it going forward.
