  We work with attracting subshifts generated by substitutions which are also
irreducible parageometric automorphisms of free groups. For such a dynamical
system, we construct a tree substitution to approximate the repelling real tree
of the automorphism. We produce images of this tree inside the Rauzy fractal
when the substitution is irreducible Pisot. We describe the contour of this
tree and compute an interval exchange transformation of the circle covering the
original substitution.
