code: def __DepthFirstSearch(node, hashes):
          
          if node.LeftChild is None:
              hashes.add(node.Hash)
          else:
              MerkleTree.__DepthFirstSearch(node.LeftChild, hashes)
              MerkleTree.__DepthFirstSearch(node.RightChild, hashes)
docs: Internal helper method.
  
          Args:
              node (MerkleTreeNode):
              hashes (list): each item is a bytearray.