pub trait Tree<T: PartialEq + Display + Debug + PartialOrd> {
// Required methods
fn iter_nodes_pre(&self, node_id: &NodeID) -> PreOrdNodes<Character<T>> ⓘ;
fn mrca(&self, nodes: Vec<NodeID>) -> &NodeID;
fn leaf_pairwise_mrca_matrix(&self) -> Vec<Vec<&NodeID>>;
}