MultiwayTree.java

static class Node {
    int key;
    String name;
    Node next;
    Node[] children;

    Node(int key, String name) {
      this.key = key;
      this.name = name;
    }

    @Override public String toString() {
      return name + " : " + key;
    }
  }
  
  static class BTree {
    Node root;
    int size;
    
    BTree(String rootName) {
      root = new Node(0, rootName);
    }
    
    Node insert(int level, String nodeName, int childCount) {
      Node refParent = root;
      for (int i = 0; i < level; i++) {
        refParent = refParent.children[0];
      }

      Node prevChildLastNode = null;
      while (refParent != null) {
        int ordinal = 0;
        refParent.children = new Node[childCount];
        for (int key = 0; key < childCount; key++) {
          refParent.children[key] = new Node(ordinal, nodeName);
          size++;
          if (key > 0) {
            refParent.children[key - 1].next = refParent.children[key];
          }
          ordinal++;
        }
        if (prevChildLastNode != null) {
          prevChildLastNode.next = refParent.children[0];
        }
        prevChildLastNode = refParent.children[childCount-1]; 
        refParent = refParent.next;
      }
      return root;
    }
  }