B+ tree

A B+ tree is an m-ary tree with a variable but often large number of children per node.

The primary value of a B+ tree is in storing data for efficient retrieval in a block-oriented storage context — in particular, filesystems. This is primarily because unlike binary search trees, B+ trees have very high fanout (number of pointers to child nodes in a node, typically on the order of 100 or more), which reduces the number of I/O operations required to find an element in the tree.

Every index has its own b+ tree

Whenever data change, it will update b+ tree.

The more indexes in one table, the more costs when insertion.