The presence of complex hierarchical gravitational structures is one of the main features of the observed universe. Here, structure formation is studied both for the standard (ΛCDM) cosmological model and for the Dirac-Milne universe, a matter-antimatter symmetric universe that was recently proposed as an alternative “coasting” cosmological scenario. One-dimensional numerical simulations reveal the analogies and differences between the two models. Although structure formation is faster in the Dirac-Milne universe, both models predict that it ends shortly before the present epoch, at cosmological redshift z≈3 for the Dirac-Milne cosmology, and at z≈0.5 for the ΛCDM universe. The present results suggest that the matter power spectrum observed by the Sloan Digital Sky Survey might be entirely due to the nonlinear evolution of matter and antimatter domains of relatively small initial dimensions, of the order of a few tens of parsecs comoving at cosmological redshift z=1080.