/**
  * Simulates a coalescent tree, given a taxon list.
  *
  * @param taxa the set of taxa to simulate a coalescent tree between
  * @param model the demographic model to use
  * @return a simulated coalescent tree
  */
 public SimpleTree simulateTree(TaxonList taxa, DemographicModel model) {
   return simulator.simulateTree(taxa, model.getDemographicFunction());
 }