is the splitting bit of the node, and N 0 i / N 1 i denote the 0 / 1 subtrees. While constructing the tree we keep track of the bits that are guaranteed to be 1. For the subtree rooted at N i we denote this value by Σ(N i ). The corresonding values for the subtrees are Σ(N 0 i ) = Σ(N i ), and Σ(N 1 i ) = Σ(N i )∪{s(N i )}. We stop the recursive splitting when the number of bitstrings in B a is below a certain threshold L. We found that balancing the binary trees generally is easily possible with the descriptors and datasets that we tested.