docs: public Clustering addToClustering(Clustering clustering) {
  		if (center != null && getClusteringFeature() != null) {
  			clustering.add(getClusteringFeature().toCluster());
  		}
  		for (ClusteringTreeNode child : children) {
  			child.addToClustering(clustering);
  		}
  		return clustering;
  	}