isTreeBalanced() {
    const current = this.root;

    if (!current) {
      return true;
    }
    return (
      this._isBalanced(current._left) &&
      this._isBalanced(current._right) &&
      Math.abs(
        this._getNodeHeight(current._left) - this._getNodeHeight(current._right)
      ) <= 1
    );
  }
Verifies if the tree is balanced.