Extract Part of a Cluster Tree
DESCRIPTION:
Returns a cluster tree which is the smallest subtree of the original that contains all of the specified leaves.
USAGE: 
subtree(tree, leaves)
REQUIRED ARGUMENTS:
tree:
a cluster tree object, normally the result of a call to hclust.
leaves:
vector of objects (i.e., row numbers of the original data matrix) which should be included in the extracted subtree.
VALUE:
the smallest subtree of tree which includes all the leaves; i.e., a list which includes the components merge, height and order described under hclust. It can be used in the various summaries of cluster results, such as plclust.
SEE ALSO:
cutree , hclust , plclust , tree .
EXAMPLES: 
votes.clust <- hclust(dist(votes.repub), "ave")
# subtree including 1st and 10th objects
subtree(votes.clust, c(1,10))


mv.vote <- subtree(votes.clust, match(c("Maryland",
                   "West Virginia", "Virginia"), state.name))
plclust(mv.vote, labels = state.abb)