as.matching returns an object of class "matching" with
the following component:
matchinga two-column numeric matrix where the columns
represent the sibling pairs.
tip.label(optional) a character vector giving the tip labels
where the ith element is the label of the tip numbered i in
matching.
node.label(optional) a character vector giving the node
labels in the same order than in matching (i.e. the ith
element is the label of the node numbered i + n in matching,
with n the number of tips).
as.phylo.matching returns an object of class "phylo".