public class TreeNode {

        private int data;
        private TreeNode rightChild;
        private TreeNode leftChild;
        private static int COUNT;

        public TreeNode(int data) {
            this.data = data;
            this.rightChild = null;
            this.leftChild = null;
        }

        public static void fillInLevel(int level, TreeNode root) {

            helper( root, level);
        }



        public static void helper( TreeNode node, int level) {

            // If it's empty and within level, fill -1

            if ( node == null)
                node = new TreeNode(-1);

            if ( node.leftChild == null )
                node.setLeftChild(new TreeNode(-1));

            if ( node.rightChild == null )
                node.setRightChild(new TreeNode(-1));

            while( level > 1) {
                helper(node.leftChild, level-=1);
                helper(node.rightChild, level-=1);
            }
            return;

        }

        public TreeNode getRightChild() {
            return rightChild;
        }

        public void setRightChild(TreeNode rightChild) {
            COUNT++;
            this.rightChild = rightChild;
        }

        public TreeNode getLeftChild() {
            return leftChild;
        }

        public void setLeftChild(TreeNode leftChild) {
            COUNT++;
            this.leftChild = leftChild;
        }

        static void print2DUtil(TreeNode root, int space)
        {
            // Base case
            if (root == null)
                return;

            // Increase distance between levels
            space += COUNT;

            // Process right child first
            print2DUtil(root.rightChild, space);

            // Print current node after space
            // count
            System.out.print("\n");
            for (int i = COUNT; i < space; i++)
                System.out.print(" ");
            System.out.print(root.data + "\n");

            // Process left child
            print2DUtil(root.leftChild, space);
        }

        // Wrapper over print2DUtil()
        static void print2D(TreeNode root)
        {
            // Pass initial space count as 0
            print2DUtil(root, 0);
        }


Current result

                      -1

           7

                      -1

2

                                 -1

                      13

                                 -1

           5

                                 11

                      3

                                            31

                                 29