private void traverse(BTreeNode root){
        for(int i=0; i < root.n; i++){
            if(!root.isLeaf){
                traverse(root.child[i]);
            }
            System.out.print(root.keys[i] + " ");
        }
        if(!root.isLeaf){
            traverse(root.child[root.n]);
        }
    }
http://www.geeksforgeeks.org/b-tree-set-1-insert-2/
http://www.geeksforgeeks.org/b-tree-set-1-introduction-2/
src/com/interview/tree/BTree.java