An excitonic cluster model, which can take into account both the strong correlation effect of 3d electrons and the itinerant nature of electronic excitations, and consequently both the bound and unbound states of electrons and holes on the same footing, is applied to describe optical excitations with even symmetry in insulating cuprates, i.e. parent crystals of high-temperature superconductors. These states are observable in large-shift Raman scattering and two-photon absorption spectra.