Tree Traversal: Level Order (BFS)
Insert n distinct integers into a BST, then print the level-order traversal (top-down, left-to-right per level).
Level order = BFS with a queue: dequeue & print a node, then enqueue its left and right children.
Input: line 1 n; line 2 n integers.
Output: one line, space-separated (trailing space ignored).
Example: 5 / 50 30 70 20 40 -> 50 30 70 20 40.