* Added some more functions to BinarySearchTree.
-> Defining intial elements of newly created Trees
-> Prettyprinting trees with left-right order and * representing null nodes.

* Added pretty print to BinaryTree.py

* Fixed flake8 Linting

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Enter your message: vishal
Enter you key [1 - 26]: 7
Encrypt or Decrypt? [E/D]: e
---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-9-9d857a810c45> in <module>
     35 
     36 if __name__ == '__main__':
---> 37     main()

<ipython-input-9-9d857a810c45> in main()
     30 
     31     if choice.lower().startswith('e'):
---> 32         print(encrypt(message, key))
     33     else:
     34         print(decrypt(message, key))

<ipython-input-9-9d857a810c45> in encrypt(message, key)
      9             num = LETTERS.find(chars)
     10             num += key
---> 11             encrypted +=  LETTERS[num]
     12 
     13     return encrypted

IndexError: string index out of range

______________________________________________
Above issue was solved

Added some lines to demonstrate the use of lambda function in a more compact way.
for example directly passing the arguments to lambda function.