Create a branch-based clonal evolution tree from tree data.frame
convert.clone.to.branch(t, branch.lens = NULL,
merged.tree.node.annotation = "sample.with.nonzero.cell.frac.ci")
merged.tree data frame from clonevol
named vector of branch lengths, named according to the cluster/clone ID/name. If not provided, all branches will receive a same length
Returns the same data.frame with additional columns, including: $branches --> symbols of the branches corresponding to the clone $blengths --> branch lengths