Method insert

packages/db/src/utils/btree.ts:843–846

* Inserts `child` at index `i`. * This does not mark `child` as shared, so it is the responsibility of the caller * to ensure that either child is marked shared, or it is not included in another tree.

(i: index, child: BNode<K, V>)

   * to ensure that either child is marked shared, or it is not included in another tree.
   */
  insert(i: index, child: BNode<K, V>) {
    this.children.splice(i, 0, child)
    this.keys.splice(i, 0, child.maxKey()!)
  }

  /**
   * Split this node.