Check for continuous binary tree in kotlin

Kotlin program for Check for continuous binary tree. Here problem description and explanation.

/* 
  Kotlin program for
  Check if binary tree is continuous tree
  Using recursion
*/
// Binary Tree Node
class TreeNode
{
	var data: Int;
	var left: TreeNode ? ;
	var right: TreeNode ? ;
	constructor(data: Int)
	{
		// Set node value
		this.data = data;
		this.left = null;
		this.right = null;
	}
}
class BinaryTree
{
	var root: TreeNode ? ;
	constructor()
	{
		this.root = null;
	}
	fun absValue(num: Int): Int
	{
		if (num < 0)
		{
			return -num;
		}
		return num;
	}
	// Check tree is continuous or not
	fun isContinuous(node: TreeNode ? ): Boolean
	{
		if (node != null)
		{
			if ((node.left != null && 
                 this.absValue(node.data - node.left!!.data) != 1) || 
                 (node.right != null && 
                  this.absValue(node.data - node.right!!.data) != 1))
			{
				// Case
				// When fail continuous tree rule
				return false;
			}
			if (this.isContinuous(node.left) && 
                this.isContinuous(node.right))
			{
				return true;
			}
			// When node value is not satisfied
			//  continuous tree properties
			return false;
		}
		return true;
	}
}
fun main(args: Array < String > ): Unit
{
	// Create new tree
	val tree: BinaryTree = BinaryTree();
	/*  
	   Binary Tree
	   ------------
	       5
	     /   \
	    4     4
	   /     /  \
	  3     5    3
	   \
	    2
	        
	*/
	// Add tree node
	tree.root = TreeNode(5);
	tree.root?.left = TreeNode(4);
	tree.root?.right = TreeNode(4);
	tree.root?.left?.left = TreeNode(3);
	tree.root?.right?.right = TreeNode(3);
	tree.root?.right?.left = TreeNode(5);
	tree.root?.left?.left?.right = TreeNode(2);
	if (tree.isContinuous(tree.root) == true)
	{
		println("Continuous Tree ");
	}
	else
	{
		println("Not Continuous Tree ");
	}
	// Case 2
	/* 
	       5
	     /   \
	    4     4
	   /     /  \
	  3     5    3
	   \
	    1  <--- change value
	        
	*/
	tree.root?.left?.left?.right?.data = 1;
	if (tree.isContinuous(tree.root) == true)
	{
		println("Continuous Tree ");
	}
	else
	{
		println("Not Continuous Tree ");
	}
}

Output

Continuous Tree
Not Continuous Tree