Borexino is a large liquid scintillator experiment located at the underground INFN Laboratori Nazionali del Gran Sasso, in Italy. It was designed and built with the primary goal of real-time detection of low energy solar neutrinos, and in more than ten years of data taking it has measured all the neutrino fluxes produced in the proton-proton-chain, i.e. the main fusion process accounting for ~99% of the energy production in the Sun. Recently, after improvements and developments in both hardware and software, Borexino has provided the first observation of solar neutrinos emitted from the subdominant Carbon-Nitrogen-Oxygen (CNO) fusion cycle. One of the key aspects of the analysis is the effectiveness and the performances of the multivariate fitting technique adopted to disentangle the neutrino signals from the backgrounds present in the detector. All the crucial steps of the analysis strategy adopted to extract the interaction rate of CNO neutrinos will be described in this poster.