Tree house mystery was volume 14 in the original Boxcar Children Series.
"Created by Gertrude Chandler Warner."
"Colored by Wes Hartman ; lettered by Johnny Lowe ; edited by Johhny Lowe ; Interior layout and design by Kristen Fitzner Denton ; cover art by Mike Dubisch ; book design and packaging by Shannon Eric Denton"--T.p. verso.
Adapted from Gertrude Chandler Warner's Tree house mystery.
The four Alden children have new neighbors and they're all building a tree house.