I saw this movie one time at a kiddie matinée at the North Park Theater in San Diego in 1959 when it was released and I was 11. It was one of three features that were shown that day.
I have not seen it since but have wanted to because I am a film buff and appreciate the terrible along with the great, good and average films.
What I remember most vividly is that the more sophisticated audience members, consisting of children between 8 and 15, howled with laughter at the tree monster.
A triple bill at a theater showing 3 adventure films is something an 11 year old does not forget, but I can't remember the names of the other 2 films. (One did star George Montgomery and David Farrar.)
UPDATE: The other 2 films in this triple bill were much better. They were "Watusi," 1959, with George Montgomery and David Farrar starring and "The Angry Red Planet," 1959, with Gerald Mohr and Naura Hayden staring. Ms. Hayden has written a couple of books on health and fitness also.