Comparative biochemistry provides strong evidence for evolution by analyzing the similarities and differences in biological molecules. The table below shows the number of amino acid differences in a 100-amino-acid region of cytochrome c between four species of birds, labeled $W$, $X$, $Y$, and $Z$.

Using the molecular evidence provided, which of the proposed phylogenetic trees (Tree I, Tree II, Tree III, or Tree IV) best represents the evolutionary relationships between these four species?