  We prove that the Farrell-Jones isomorphism conjecture for non-connective
algebraic K-theory for a discrete group G and a coefficient ring R holds true
if G belongs to the class of groups acting on trees, under certain conditions
on G (see theorem 0.5 below) and if the coefficient ring R is either regular or
hereditary, depending on the structure of G. Our result is weaker than the
result that has been established in [15] which says that these groups verify
the conjecture for any coefficient ring, see remark 0.6 below.
