class Node:
  def __init__(self,key):
    self.left = None
    self.right = None
    self.val = key
    
# specifying the root node
root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)

# Note above that by default, the daughter nodes are None. We don't need to specify them
