Compact, simple tree representation

The NeXML file format has a rather verbose way of representing trees. For example, this tree:

Can be represented as a Newick string like so:


But in NeXML it becomes this:


For small trees - or small sets of trees - the advantages of NeXML outweigh this verbosity, but for big trees or large sets (e.g. from a Markov chain) this becomes a problem.