// Start of function levelOrder
    this.levelOrder = function(root) {
    if (!root) return;

        const queue = [];
        queue.push(root);

        while (queue.length > 0) { 
            const levelSize = queue.length; 

        for (let i = 0; i < levelSize; i++) { 
        const node = queue.shift(); 
        process.stdout.write(node.data + ' '); 

        if (node.left) queue.push(node.left); 
        if (node.right) queue.push(node.right);  
        }
        }  
    }; // End of function levelOrder