Comparing trees to differentiate or group them can help researchers to see patterns of evolution. Multiple trees of a single gene tracked across species or strains can reveal differences in how that gene is changing across species. At the core of these approaches are metrics of distances between trees. In this recipe, we'll calculate one such metric to find pairwise differences between 20 different gene trees in 15 different species—hence, 15 different tips with identical names in each tree. Such similarity in trees is usually needed to compare and get distances, and we can't do an analysis like this unless these conditions are met.