  We study cutoff effects at tree-level of perturbation theory for standard
Wilson and Wilson twisted mass fermionic lattice actions with Nf=2 flavour
degenerate quarks. The discretization effects are investigated by computing the
mass spectrum and decay amplitudes for different hadron interpolating fields
and the scaling behaviour towards the continuum limit is analyzed. It is shown
that the Wilson and the mass average methods are equivalent and lead to O(a)
improved R5-parity even lattice observables. We also demonstrate that automatic
O(a) improvement works in case of Wilson twisted mass fermions at maximal twist
and that this improvement is realized even if the condition of maximal twist is
achieved only up to O(a) cutoff effects. We demonstrate that in the chiral
limit standard Wilson fermions show scaling violations of O(a^2) while for
maximally twisted mass fermions these violations are only of O(a^4). For our
analytical calculations, lattices with sizes L=aN and periodic boundary
conditions in the spatial directions have been chosen while infinite extension
in the time direction is considered.
