code: def test_is_tree(self):
      assert nx.is_tree(self.T2)
      assert nx.is_tree(self.T3)
      assert nx.is_tree(self.T5)
  
imports: import pytest
  import networkx
label_desc: Use image node_id 6 for calling the TestTreeRecognition obj's underlying member method code with example usage: obj.test_is_tree() without return types