  An approximate numerical approach to spin models is proposed, in which the
original lattice is transformed into a tree. This method is applied to the
Edwards-Anderson spin glass model in two and three dimensions. It captures the
characteristics of each individual sample and reproduces various qualitative
features of sample averaged quantities similar to those that have been observed
in previous Monte Carlo simulations. For example, from the Binder parameter for
various system sizes as a function of the temperature we obtain Tc ~ 1.0 with
\nu ~ 1.85, in reasonable agreement with previous Monte Carlo simulations. The
present approximation yields the trivial structure for the overlap distribution
function.
