Does rotational simple harmonic motion occur when there is linear restoring torque?

Rotational simple harmonic motion occurs when there is a linear restoring torque given by Τr=-Kθ, where θ is the angular displacement from equilibrium. The period of the resulting rotational oscillation is given in ogy with T=2π(m/k)^.5 by T=2π(I/K)^.5. How is the equation T=2π(mL/mg)^.5=2π(L/g)^.5 derived by treating the simple pendulum as a rotating system with the suspension point as the pivot. Note that for small angles, sinθ ≈ θ.