code: def add_leaf(self, leaf_blob):
          
          self.leaves.append(MerkleLeaf(len(self.leaves), leaf_blob))
docs: Adds a leaf to the list of leaves.  Does not build the tree so call
          `build()` to construct the rest of the tree from the added leaves.
  
          :param leaf_blob: the leaf payload to add.  should be a hashable object