private String printTree(ClassifierTreeNode parent) {
        String line = "\n|";
        for (int i = 0; i < parent.getLevel(); i++) {
            line += "-";
        }
        line += parent.getFeature().getName();
        if (!parent.getChildren().isEmpty()) {
            for (ClassifierTreeNode node : parent.getChildren()) {
                line += printTree(node);
            }
        }
        return line;
    }