In the following paper we are considering Hamiltonians with multiband structure. In this case the important quantities to characterize topological states are non-Abelian connection matrix, Berry curvature and Wilson loop. We calculated some of the Wilson loops and showed that their set has a group structure and is isomorphic to $\pi_1(T^2)=\mathbb{Z}\times \mathbb{Z}$. It is shown how to get the same results using the facts known in differential geometry.