The Word of Teregor (1914) by Guy Ridley (1885-1947) is an early British fantasy novel of sentient trees. The trees converse in moots and are unfriendly to men. One of the trees is called Enteth.

“No one but a real lover of trees could write of them as Mr. Ridley has done.” — review in the Westminster Gazette. “A suggestive and original voice among the babel of modern literature” — review in The Daily Telegraph.

An obvious inspiration for J.R.R. Tolkien’s Ents, circa 1938, you might think. Though I doubt that would be provable now — and anyway there are more obvious and earlier possibilities. Such as an aside in Shakespeare’s Macbeth (“Who can impress the forest, bid the tree | Unfix his earthbound root?” ‘impress’ = to strongarm a man into armed service in an Army). This might perhaps be Shakespeare’s nod to Taliesin’s magnificent poem “The Battle of the Trees” (Cad Goddeu), in which many types of trees are enchanted into a marching army of trees. Tolkien and his circle had surely found time to notice Taliesin by 1938 — though I imagine that Tolkien would have been professionally wary of seeming to endorse the authenticity of the late Welsh ‘bardic’ songs.

There’s also a prime example from Tolkien’s childhood, the “Attack of the trees” from the famous The Wizard of Oz, here depicted in 1900 by Denslow…

Anyway, the full novel is at the link above.