Converts a hierarchical clustering encoded in the matrix Z (by linkage) into an easy-to-use tree object. The reference r to the root ClusterNode object is returned.
Each ClusterNode object has a left, right, dist, id, and count attribute. The left and right attributes point to ClusterNode objects that were combined to generate the cluster. If both are None then the ClusterNode object is a leaf node, its count must be 1, and its distance is meaningless but set to 0.
Note: This function is provided for the convenience of the library user. ClusterNodes are not used as input to any of the functions in this library.