The procedure B-tree-Split-Child takes as input a nonfull internal node x (as-sumed to be in main memory) ,an index I , and a node y (also assumed to be in main memory) such that y = ci[x] is a full child of x. The procedure then splits this child in two and adjusts x so that it has an additional child. (To split a full root ,we will first make the root a child of a new empty root node , so that we can use B-Tree-Split-Child . The tree thus grows in height by one ; splitting is the only means by which the tree grows)
Figure 18.5 illustrates this process, the full node y is split about its median key S, which is moved up into y ‘s parent node x .Those keys in y that are greater than the median key are placed in a new node z ,which is made a new child of x.