input: Write a python function to perform preorder traversal of a binary tree and print the nodes. 
  assert preorder_traversal(root1)==None # Assuming root1 is the root of a binary tree with preorder traversal [1,2,4,5,3]
  assert preorder_traversal(root2)==None # Assuming root2 is the root of a binary tree with preorder traversal [10,20,30,40,50]
output: def preorder_traversal(root):
      if root is None:
          return
      
      # Print the data of the node
      print(root.data)
      
      # Recur on left subtree
      preorder_traversal(root.left)
      
      # Recur on right subtree
      preorder_traversal(root.right)