AttributeError: hierarchical

[anuraglahon16]

ef StartCrew(prompt):

task1 = Task(
  description=f"""Write a blog post of {prompt}. """,
  agent=writer,
  expected_output="an article under 100 words."
)

task2 = Task(
  description=("list review comments for improvement from the entire content of blog post to make it more viral on social media."
                "Make sure to check with a human if your comment is good before finalizing your answer."
            ),
  agent=reviewer,
  expected_output="Builtin points about where need to be improved.",
  human_input=True,
)
# Establishing the crew with a hierarchical process
project_crew = Crew(
    tasks=[task1, task2],  # Tasks to be delegated and executed under the manager's supervision
    agents=[writer, reviewer],
    manager_llm=llm,
    process=Process.hierarchical  # Specifies the hierarchical management approach
)

result = project_crew.kickoff()

File "/Users/anuraglahon/opt/anaconda3/envs/my_env/lib/python3.11/threading.py", line 1038, in _bootstrap_inner
self.run()
File "/Users/anuraglahon/opt/anaconda3/envs/my_env/lib/python3.11/threading.py", line 975, in run
self._target(*self._args, **self._kwargs)
File "/Users/anuraglahon/Documents/feedback/crewai_panel.py", line 43, in initiate_chat
StartCrew(message)
File "/Users/anuraglahon/Documents/feedback/crewai_panel.py", line 124, in StartCrew
process=Process.hierarchical # Specifies the hierarchical management approach
^^^^^^^^^^^^^^^^^^^^
File "/Users/anuraglahon/opt/anaconda3/envs/my_env/lib/python3.11/enum.py", line 784, in getattr
raise AttributeError(name) from None
AttributeError: hierarchical