a) Binary tree dendrogram. Each superior node supports several lower pairs. Different colors highlight the biggest nodes. b) Trends. The ellipses are the representation in PC space of the nodes of same roman letter in panel a). The nodes I and IV represent the equation for the Blue and Red trends. The contours are the projected ellipsoids. The dotted lines are the projected cylinder obtained through the secondary eigenvectors of the variance-covariance matrix of the I and IV nodes.