This paper deals with a measurement campaign conducted in the urban area of Rome (Italy), with the aim to analyse the propagation effects of vegetation (lime trees) on one of the mmWave signals under investigation to be exploited in 5G radio systems. Experimental measurements lead to the channel characterization in presence of a 500 MHz bandwidth signal transmitted on a carrier of 33 GHz, through calculation of large scale and small scale parameters as time delay, delay spread, coherence bandwidth, and signal attenuation. Experimental results are compared with some empirical models, proposed in literature, to estimate excess loss in presence of vegetation.