Figure 2. Simplified example of a BK-tree built on five UMIs.

These UMIs are “ATAA”, “AAAA”, “CCGG”, “AAAT”, and “ATTA”, inserted in that order into the tree. Only nodes that are shaded are visited when searching for UMIs within 1 edit of “AAAG”. Each edge between two UMIs u and v has a number that indicates d(u, v), the Hamming distance between u and v.