1. A non-transitory computer readable medium comprising machine readable instructions for: accessing a representation of a target tree, the representation having edges and vertices; identifying a vertex in the representation that includes a first out-edge, a second out-edge and an in-edge, where the second out-edge is a terminal edge and where a first vertex defines one end of the first out-edge and a second vertex defines one end of the in-edge, and where the vertex, the first vertex, and the second vertex are different from each other; and introducing an edge to the representation that extends between the first vertex and second vertex, where the target tree comprises a human airway tree.