This function adds a tip to all branches to the tree and returns a
a list of trees as an object of class "multiPhylo".
Usage
add.everywhere(tree, tip.name)
Arguments
tree
an object of class "phylo".
tip.name
a string containing the name of the tip to add.
Value
a list of trees as an object of class "multiPhylo". Since the
tip can be added to any branch, the length of the list is equal to the
number of edges in tree.