Distribution of the number of peaks per GRB for the Fermi/GBM catalogue. The observed and expected counts are displayed in orange and blue, respectively. The histogram bins were grouped to ensure a minimum number of 15 expected counts per bin. The dashed black line shows the best-fitting model of mixture of two exponentials. The blue and grey regions respectively show the 50% and 90% model confidence interval obtained from sampling the posterior distribution of the model parameters computed through Markov chain Monte Carlo simulations.