  We construct merger trees based on the extended Press-Schechter theory (EPS)
in order to study the merger rates of dark matter haloes over a range of
present day mass ($10^{10}M_{\sun}\leq M_0 \leq10^{15}M_{\sun}$), progenitor
mass $(5\times10^{-3}\leq \xi \leq1$) and redshift ($0\leq z\leq 3$). We used
the first crossing distribution of a moving barrier of the form
$B(S,z)=p(z)+q(z)S^{\gamma}$, proposed by Sheth & Tormen, to take into account
the ellipsoidal nature of collapse. We find that the mean merger rate per halo
$B_m/n$ depends on the halo mass $M$ as $M^{0.2}$ and on the redshift as
$(\mathrm{d}\delta_c(z)/\mathrm{d}z)^{1.1}$. Our results are in agreement with
the predictions of N-body simulations and this shows the ability of
merger-trees based on EPS theory to follow with a satisfactory agreement the
results of N-body simulations and the evolution of structures in a hierarchical
Universe.
