Figure 2.

Hierarchical Ensemble. (a) An example of a classical ensemble method, and (b) an example of a hierarchical ensemble method, where red rectangle represents the base classifier with wrong classification result, and green rectangle represents the base classifier with correct classification result. Taking nine base classifiers as an example, the classical ensemble method cannot give correct prediction results when the number of correct base classifiers is less than half of the total number of classifiers. Through the continuous combination of base classifiers, the hierarchical ensemble method can still give correct prediction results even if the number of correct classifiers is less than half.