class TreeNode {
  constructor(val) {
    this.val = val;
    this.left = null;
    this.right = null;
  }
}

class BinarySearchTree {

  constructor() {
    this.root = null;
  }

  insert(val, currentNode=this.root) {
    if (currentNode === null) {
      currentNode = new TreeNode(val);
    } else if (val < currentNode.val) {
      this.insert(val, currentNode.left);
    } else {
      this.insert(val, currentNode.right);
    }
  }

This is my code: I am getting the following error: TypeError: Cannot read properties of null (reading 'val')
My code doesn't seem to be updating the value of this.root or currentNode and I am not sure why.