This paper considers the problem of classification tree based data analysis. Among the topics discussed in the paper axe: growing a classification tree using CART style exhaustive search for spl/ts, selecting the tight size for the tree using minimal cost-complexity cross-validation pruning, and examples of the application of classification trees.The algorithms are implemented in Dyalog APL.Application example is based on data from vibration monitoring equipment installed on a Nuclear Power Plant in Novovoronehz, Russia and includes classification of vib~tion spectra of steam generators or coolant pumps and classification of vibration spectra of steam generators of different coolant loops.