Given two binary search trees with root nodes as `bst1`

and `bst2`

of size `n`

and `m`

, write a program to return an array of integers that contains all the elements of `bst1`

and `bst2`

in non-decreasing order.

**Problem Note**

- The expected time complexity is O(
`m+n`

).

**Example 1**

```
Input: 3 4
/ \ / \
2 5 1 6
Output: [1, 2, 3, 4, 5, 6]
Explanation: The resultant binary tree contains all the elements of bst1 and bst2 in non-decreasing order.
```

**Example 2**

```
Input: 3 6
\ / \
4 2 10
Output:[2, 3, 4, 6, 10]
Explanation: Both bst1 and bst2 are combined to return the BST having all the elements of bst1 and bst2 in non-decreasing order.
```