This paper presents a simplified RET model derived from path loss and directional spectrum measurements in vegetation media at 11 and 20 GHz. Thus, a simplified extraction procedure for the inputs parameters based on the method foreseen by the ITU-R P.833-8, however for isolated vegetation volumes, is proposed. Results for specific measurements aimed at the extraction of the RET model parameters, are subsequently presented and discussed. The extraction method relies on a limited set of propagation measurements to find and optimise the RET input parameters. Specific measurements of the received signal directional profile are used to show the applicability of the method. This parameter evaluation method is tested and assessed based on the received signal directional profile measurements performed in Populous trees at 11.2 and 20 GHz.