“The Tree-Men of M’Bwa” by Donald Wandrei is one of those wonderful Weird Tales gems that I love to happen upon. The story was published in February 1932. It has only been reprinted in Wandrei collections, which surprises me. The story is so good, so weird in the true Lovecraftian sense. Why haven’t the great collectors like Peter Haining or Stephen Jones used it? Why haven’t the Cthulhu Mythos fanboys not jumped all over it? Why reprint “Dracula’s Guest” yet again while this story rests ignored?
The story is about an African explorer who comes across Richards of the missing Angley & Richards expedition. The man looks old and has lost his legs. He tells what happened: the party split in two and Richards had gone in the direction of the Mountains of the Moon. His Neguchi bearers try to talk him out of going in that direction and desert him. He goes on anyway and comes to a plain where a ring of weird trees circle a shining pyramid. Coming closer he sees the trees all look like men. M`Bwa appears:
“…But there he was all of a sudden, not fifty yards away, a horribly wrinkled old black, with a face as pasty as the gray ground, and a blank look in his eyes. What’s more, he was coming straight at me, no mistake about it… in complete sheer terror, I let him have it, both barrels full in the chest. I saw the bullets crash clear through him, but he didn’t even falter, and not a drop of blood came from the livid flesh around the hole. Then I turned to run and he was on me like the wind. He was cold, his eyes were dead like a corpse’s, and I knew I was up against something beyond the most frightful dream. Never a sound did he make, never a light of life or intelligence shone in his dead eyes; he moved like living death, soulless, stiff, and his flesh was like ice but his strength was terrific.” 
M`Bwa chases him down, and pours a strange liquid down his throat. Richards is planted next to the last poor soul to be caught, a man who has almost completely turned into a tree. He learns that M`Bwa serves an evil space entity called the Master inside the shining pyramid. Now he knows his fate and prays Angley will come in time to rescue him. Angley does come, cutting off M’Bwa`s head. The Master floats out of his pyramid, a dark and evil thing, and revives M’Bwa. Angley attacks again, cutting M’Bwa in half. The two men escape, though Angley dies later. Not much is explained, leaving the reader to wonder about these strange events.
Wandrei has one more surprise in store but I won’t ruin it for you. Read “The Tree-Men of M’Bwa” and thrill as Weird Tales readers did back in 1932.