We propose a simple method to construct integral periodic mask and corresponding scaling step functions that generate non-Haar orthogonal MRA on the local field F (s) of positive characteristic p. To construct this mask we use two new ideas. First, we consider local field as vector space over the finite field GF (p s ). Second, we construct scaling function by arbitrary tree that has p s vertices. By fixed prime number p there exist p s(p s −2) such trees.