Difference between sums of odd and even levels in n-ary tree

import java.util.Vector;
// Java program for
// Difference between sums of odd level and even 
// level nodes in an N-ary Tree
class TreeNode
{
	public int key;
	public Vector < TreeNode > child;
	public TreeNode(int key)
	{
		// Set node key
		this.key = key;
		// Create memory of TreeNode child
		this.child = new Vector < TreeNode > ();
	}
	public void addChild(int key)
	{
		// Create a new node
		TreeNode node = new TreeNode(key);
		// Add node into child
		this.child.add(node);
	}
}
public class NAryTree
{
	public TreeNode root;
	public int even;
	public int odd;
	public NAryTree()
	{
		this.root = null;
		this.even = 0;
		this.odd = 0;
	}
	public void findLevelSum(TreeNode node, int level)
	{
		if (node == null)
		{
			return;
		}
		int i = 0;
		if (level % 2 == 0)
		{
			// Sum of even level node
			this.even += node.key;
		}
		else
		{
			// Sum of odd level node
			this.odd += node.key;
		}
		// iterating the child of given node
		while (i < node.child.size())
		{
			// Visit to child subtree
			findLevelSum(node.child.get(i), level + 1);
			// Change child node
			i++;
		}
	}
	public void levelSumDifference()
	{
		this.even = 0;
		this.odd = 0;
		this.findLevelSum(this.root, 0);
		System.out.println(" Difference : " + (this.even - this.odd));
	}
	public static void main(String[] args)
	{
		NAryTree tree = new NAryTree();
		/*
		           10
		          /   \
		         /     \
		        /       \   
		       8         5
		      /|\      /|\ \ 
		     / | \    / | \ \
		    -2 1  6  7 18 3  4
		      / \           /| \
		     9  11         2 1  3
		       /  \
		      17   12   
		    -----------------------
		    Constructing N-Ary tree
		*/
		// First element of tree
		tree.root = new TreeNode(10);
		tree.root.addChild(8);
		tree.root.addChild(5);
		// Add child node [-2,1,6] in node (8)
		tree.root.child.get(0).addChild(-2);
		tree.root.child.get(0).addChild(1);
		tree.root.child.get(0).addChild(6);
		// Add child node [9,11] in node (1)
		tree.root.child.get(0).child.get(1).addChild(9);
		tree.root.child.get(0).child.get(1).addChild(11);
		// Add child node [17  12] in node (11)
		tree.root.child.get(0).child.get(1).child.get(1).addChild(17);
		tree.root.child.get(0).child.get(1).child.get(1).addChild(12);
		// Add child node [7 18 3 4] in node (5)
		tree.root.child.get(1).addChild(7);
		tree.root.child.get(1).addChild(18);
		tree.root.child.get(1).addChild(3);
		tree.root.child.get(1).addChild(4);
		// Add child node [2,1,3] in node (4)
		tree.root.child.get(1).child.get(3).addChild(2);
		tree.root.child.get(1).child.get(3).addChild(1);
		tree.root.child.get(1).child.get(3).addChild(3);
		/*
		           10                Level 0
		          /   \
		         /     \   
		        /       \   
		       8         5           Level 1
		      /|\      /|\ \ 
		     / | \    / | \ \
		    -2 1  6  7 18 3  4       Level 2
		      / \           /| \
		     9  11         2 1  3    Level 3
		       /  \
		      17   12                Level 4
		    -----------------------
		    
		    Even level node sum 
                 [10 + (-2) + 1 + 6 + 7 + 18 + 3 + 4 + 17 + 12] = 76
		    Odd level node sum
                [8 + 5 + 9 + 11 + 2 + 1 + 3] = 39
		    ----------------------------------------
		    (76-39) = 37
		*/
		tree.levelSumDifference();
	}
}

Output

 Difference : 37