code: def tree():
      Phylo = pytest.importorskip("Bio.Phylo")
      tree_file = io.StringIO(TREE_NEXUS)
      trees = list(Phylo.parse(tree_file, "nexus"))
      assert len(trees) == 1
      return trees[0]
  
imports: import io
  import re
  import pytest
  import torch
  import pyro
  from pyro.distributions import CoalescentTimes, CoalescentTimesWithRate
  from pyro.distributions.coalescent import CoalescentRateLikelihood, CoalescentTimesConstraint, _sample_coalescent_times, bio_phylo_to_times
  from pyro.distributions.util import broadcast_shape
  from tests.common import assert_close
label_desc: Use image node_id 10 for calling a global function with example usage: tree() and returns: trees