The output of this function mirrors the output of the C5.0
command line version.
The terminal nodes have text indicating the number of samples
covered by the node and the number that were incorrectly
classified. Note that, due to how the model handles missing
values, the sample numbers may be fractional.
There is a difference in the attribute usage numbers between
this output and the nominal command line output. Although the
calculations are almost exactly the same (we do not add 1/2 to
everything), the C code does not display that an attribute was
used if the percentage of training samples covered by the
corresponding splits is very low. Here, the threshold was
lowered and the fractional usage is shown.