It is known that ferroelectric single crystals can be turned from a polydomain to a monodomain state by the application of an electric field. Here we report an unexpected opposite effect: the formation of through-the-crystal polydomain pattern in a monodomain BaTiO3 crystal in response to the applied electric field favoring the initial orientation of the polarization. The effect is achieved for special electric field direction which equally selects two domain states, which are present in the polydomain pattern. At the formation of the pattern, the new wedge domains propagate from the sides of the sample in the direction transverse to the electric field. The observations are rationalized in terms of a simple analytical model treating energies of competing domain configurations as functions of the electric field. The results of the analytical treatment are supported by phase field modeling.