(a) A nonlinear function (black) with its prediction (gray) based on a regression tree. (b) Splits in the regression tree minimize mean square error (MSE), which is shown here for all possible positions of the first split. (c) The full regression tree for the prediction shown in a. For each split, the absolute MSE and relative (to the first node) rMSE is shown along with the difference in successive rMSE values, a. The tree was built with cutoff of a = 0.01, which terminates the growth of the tree at the dashed line.