# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def getAllElements(self, root1: TreeNode, root2: TreeNode) -> List[int]:
        res1 = self.dfs(root1, [])
        res2 = self.dfs(root2, [])
        if res1 is None or res2 is None:
            return res1 if res1 is not None else res2
        res = []
        left,right = 0, 0
        while left < len(res1) and right < len(res2):
            if res1[left] <= res2[right]:
                res.append(res1[left])
                left += 1
            else:
                res.append(res2[right])
                right += 1
        if left <= len(res1) -1:
            for i in range(left, len(res1)):
                res.append(res1[i])
        if right <= len(res2)-1:
            for i in range(right, len(res2)):
                res.append(res2[i])
        return res
    def dfs(self, root, res):
        if root is None:
            return 
        self.dfs(root.left, res)
        res.append(root.val)
        self.dfs(root.right, res)
        return res