This is a tree of files and directories which is used in Subversion python tests. It is called so because of files of this tree which are called after names of different letters of the Greek alphabet. This tree can be represented as follows:
Repository Root
____|____
/ \
/ \
/ \
A iota
_______________________//|\
/ ______________/ | \_____________
mu / | \
/ | \
B C D
_____/|\_____ _____________/|\
/ | \ / | \
/ | \ / / \
lambda | F / / \
E gamma / \
/ \ / \
/ \ ________/ \________
alpha beta / \
/ \
/ \
G H
________/|\_______ _______/|\______
/ | \ / | \
/ | \ / | \
/ | \ / | \
pi rho tau chi psi omega