Trie

A trie is a n-ary tree which is generally used to retrieval of things such as dictionaries.

Dictionary Example
Using the The trie starts out with a root node which points to the start letter nodes of the alphabet. If you add a new word, find the first letter of the node and keep adding node for that specific letter as you go down in the trie. Once you reach the end, tag the specific node you have reached to denote the path to this node is a word.

inserting in it and into the tree after 'in' is inserted. /     i       \ n*

tree after 'it' is inserted /     i     / \ n* t* tree after 'into' is inserted /     i     / \ n* t*     \ t      \ o*

If we do a inorder traversal on this tree and keep track of the nodes passed we can get an alphabetically sorted list of words.