965\. Univalued Binary Tree

Easy

A binary tree is **uni-valued** if every node in the tree has the same value.

Given the `root` of a binary tree, return `true` _if the given tree is **uni-valued**, or_ `false` _otherwise._

**Example 1:**

![](https://assets.leetcode.com/uploads/2018/12/28/unival_bst_1.png)

**Input:** root = [1,1,1,1,1,null,1]

**Output:** true

**Example 2:**

![](https://assets.leetcode.com/uploads/2018/12/28/unival_bst_2.png)

**Input:** root = [2,2,2,5,2]

**Output:** false

**Constraints:**

*   The number of nodes in the tree is in the range `[1, 100]`.
*   `0 <= Node.val < 100`