code: def _build_tree(self):
      if self._tree is None:
          self._tree = self.run_pipeline(
              [],
              """
              def decorator(fun):  # DefNode
                  return fun       # ReturnStatNode, NameNode
              @decorator           # NameNode
              def decorated():     # DefNode
                  pass
              """,
          )
      return self._tree
  
file_path: catboost/contrib/tools/cython/Cython/Compiler/Tests/TestTreePath.py
imports: import unittest
  from Cython.Compiler.Visitor import PrintTree
  from Cython.TestUtils import TransformTest
  from Cython.Compiler.TreePath import find_first, find_all
  from Cython.Compiler import Nodes, ExprNodes
label_desc: Use image node_id 1 for calling the TestTreePath obj's underlying member method code with example usage: obj._build_tree() and returns: self