We see humanoid trees or plants in SFF universe all the time. They can walk and talk. Some are highly intelligent, others are not. Some are mythical creatures, others are aliens.
Examples can be:
Ent (The Lord of the Rings: The Two Towers, 1954)
Huorn (The Lord of the Rings: The Two Towers, 1954)
Groot (Marvel's Tales to Astonish #13, 1960)
Tree of Cheem (new Doctor Who S01E02, 2005)
Eliza (new Doctor Who S10E04, 2017)
Wildvine (Ben 10 S02E07, 2006)
Methanosian (Ben 10, Late 00s)
Highbreed Tree Monster (Ben 10, Late 00s)
Treefolk (Magic: The Gathering, post-1993)
Which Science Fiction or Fantasy work introduced the idea of walking-and-talking humanoid trees/plants?