extract a single multiPhylo object containing all trees in the nexml
Details
Note that this method collapses any hierarchical structure that may have been present as multiple trees nodes in the original nexml (though such a feature is rarely used).  To preserve that structure, use get_trees instead.
Examples
comp_analysis <- system.file("examples", "comp_analysis.xml", package="RNeXML")
nex <- nexml_read(comp_analysis)
get_flat_trees(nex)
#> 1 phylogenetic tree