title: understanding the tree view in apache airflow
body: <p>I setup the dag from the <a href="https://airflow.apache.org/tutorial.html" rel="nofollow noreferrer">https://airflow.apache.org/tutorial.html</a> as is, the only change being that I have set the dag to run at an interval of 5 minutes with a start date of 2017-12-17 T13:40:00 UTC. I enabled the dag before 13:40, so there was no  backfill and my machine is running on UTC.  The dag ran as expected(i.e at an interval of 5 minutes starting at 13:45 UTC) </p>
  
  <p>Now, when I go to the tree view, I am failing to understand the graph. There are 3 tasks in total. 'sleep'(t2) has upstream set to 'printdate' (t1) and  'templated'(t3) too has upstream set to 'printdate'(t1). Then why is the graph showing two 'printdate's ?? Are they separate task instances of that task? If yes, then how do I make sure that only 1 task instance of t1 runs (diamond pattern). There are also 4  green rectangular boxes(with two 'printdate's), instead of 3.</p>
  
  <pre><code># t1, t2 and t3 are examples of tasks created by instantiating operators
  t1 = BashOperator(
      task_id='print_date',
      bash_command='date',
      dag=dag)
  
  t2 = BashOperator(
      task_id='sleep',
      bash_command='sleep 5',
      retries=3,
      dag=dag)
  
  templated_command = """
      {% for i in range(5) %}
          echo "{{ ds }}"
          echo "{{ macros.ds_add(ds, 7)}}"
          echo "{{ params.my_param }}"
      {% endfor %}
  """
  
  t3 = BashOperator(
      task_id='templated',
      bash_command=templated_command,
      params={'my_param': 'Parameter I passed in'},
      dag=dag)
  
  t2.set_upstream(t1)
  t3.set_upstream(t1)
  </code></pre>
  
  <p>Second, why is the time above the dag runs (green circles), showing 8.40, 8.45 - ? What time/timezone is that? I have set start_date for the dag to 13.40 and my machine set to UTC.</p>
  
  <p><a href="https://i.stack.imgur.com/rLtHV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rLtHV.png" alt="enter image description here"></a></p>