Use this if you are using igraph from R
hrg_tree creates the corresponsing igraph tree of a hierarchical
random graph model.
hrg_tree(hrg)
| hrg | A hierarchical random graph model. | 
An igraph graph.
Other hierarchical random graph functions: consensus_tree,
fit_hrg, hrg-methods,
hrg, predict_edges,
print.igraphHRGConsensus,
print.igraphHRG, sample_hrg