1305. All Elements in Two Binary Search Trees

Python

class Solution:
    def getAllElements(self, root1: TreeNode, root2: TreeNode) -> List[int]:

        tree1 = self._travel(root1, [])
        tree2 = self._travel(root2, [])

        return sorted(tree1 + tree2)


    def _travel(self, node, result):
        if not node:
            return result

        self._travel(node.left, result)
        result.append(node.val)
        self._travel(node.right, result)

        return result