What is B-Tree?

The database server uses a B-tree structure to organize index information. B-Tree generally has following types of index pages or nodes:

root node: A root node contains node pointers to branch nodes which can be only one.
branch nodes: A branch node contains pointers to leaf nodes or other branch nodes which can be two or more.
leaf nodes: A leaf node contains index items and horizontal pointers to other leaf nodes which can be many.