Non leaf nodes of B+ tree structure form a : 

The correct answer is Multilevel sparse indices.

Key Points

• Non-leaf nodes of a B+ tree structure form multilevel sparse indices, which are crucial for its efficiency and performance.
• In a B+ tree, all the actual data records are stored in the leaf nodes, while the non-leaf nodes (or internal nodes) store the keys that act as pointers to guide the search process.
• The non-leaf nodes do not store every key, only enough to direct the search to the appropriate leaf node, making the indices sparse.
• This structure helps in reducing the height of the tree, thus speeding up the search, insert, and delete operations.
• Multilevel indexing means that the tree is structured in multiple levels (root, intermediate levels, and leaf nodes), where each level helps narrow down the search space progressively.
• The B+ tree is a balanced tree, meaning all the leaf nodes are at the same level, which ensures consistent and predictable performance.

Additional Information

• B+ trees are widely used in database indexing and file systems due to their efficiency in handling large amounts of data.
• They are an extension of B-trees, with the primary difference being that in B+ trees, all values are stored at the leaf level, and internal nodes only store keys.
• This structure ensures that sequential traversal of the data can be done efficiently by following the linked leaf nodes.
• Because of the multilevel sparse indexing, B+ trees are well-suited for range queries and ordered traversals.
• B+ trees maintain balance by splitting and merging nodes as necessary during insertions and deletions, ensuring that the tree remains balanced with minimal height.