An implementation of M-trees. M-trees are an index structure for metric data (ie. data for which we can define a distance function). This implementation supports efficient incremental insertion and range queries.
Ciaccia, P., Patella, M., & Zezula, P. (1997, August). M-tree: An efficient access method for similarity search in metric spaces. In Vldb (Vol. 97, pp. 426-435).