Check if a binary tree is BST or not in scala

Scala program for Check if a binary tree is BST or not. Here mentioned other language solution.

// Scala program for
// Check if a binary tree is BST or not
class TreeNode(var data: Int,
	var left: TreeNode,
		var right: TreeNode)
{
	def this(data: Int)
	{
		this(data, null, null)
	}
}
class BinaryTree(var root: TreeNode)
{
	def this()
	{
		this(null)
	}
	def isBst(node: TreeNode, 
              l: TreeNode, 
              r: TreeNode): Boolean = {
		if (node != null)
		{
			if (l != null && l.data > node.data || 
                r != null && r.data < node.data)
			{
				// When parent node are not form of binary tree
				return false;
			}
			return (isBst(node.left, l, node) && 
                    isBst(node.right, node, r));
		}
		return true;
	}
	// Display tree elements in order form
	def inorder(node: TreeNode): Unit = {
		if (node != null)
		{
			inorder(node.left);
			// Print node value
			print("  " + node.data);
			inorder(node.right);
		}
	}
}
object Main
{
	def main(args: Array[String]): Unit = {
		var tree: BinaryTree = new BinaryTree();
		/*
		  Binary Tree
		  ---------------
		          15
		          / \
		         /   \
		        10   24
		       /    /  \
		      9    16   30
		*/
		// Add tree node
		tree.root = new TreeNode(15);
		tree.root.left = new TreeNode(10);
		tree.root.right = new TreeNode(24);
		tree.root.right.right = new TreeNode(30);
		tree.root.right.left = new TreeNode(16);
		tree.root.left.left = new TreeNode(9);
		// Display Tree elements
		tree.inorder(tree.root);
		if (tree.isBst(tree.root, null, null))
		{
			println("\n  Yes ");
		}
		else
		{
			println("\n  No ");
		}
		/*
		  Add new node 25 in binary tree
		  -----------------------
		      15
		      / \
		     /   \
		    10   24
		   /    /  \
		  9    16   30
		         \
		          25
		*/
		tree.root.right.left.right = new TreeNode(25);
		// Display Tree elements
		tree.inorder(tree.root);
		if (tree.isBst(tree.root, null, null))
		{
			println("\n  Yes ");
		}
		else
		{
			println("\n  No ");
		}
	}
}

Output

  9  10  15  16  24  30
  Yes
  9  10  15  16  25  24  30
  No