By using adaptive coding, this method will let us use higher-order modeling without paying any penality for added statistics.
Tree is a binary tree with a sibling property.
A binary tree such that every node has a weight assigned to it. The tree also exhibits the sibling property if the nodes can be listed in order in increasing weight and if every node appears adjacent to it sibling in the list. The sibling property is important in adaptive Huffman coding in that it helps show what we need to do to a Huffman tree when it is time to update the counts. Maintaining the sibling property during an update assures that we have a Huffman tree before and after the counts are adjusted. Then move up to the parent node.