# Binary Tree Level Order Traversal (BFS)
Given a binary tree, return its node values grouped level by level (a BFS traversal).
Module 1's Tree Traversal lesson and Mock 3 are both DFS-heavy (in/pre/post-order, LCA, diameter) — this fills the missing BFS-on-trees gap with the queue-based level-order pattern.
The tree is passed as a nested list, not a custom class, for gradability: `node = [value, left_or_None, right_or_None]`, e.g. `[3, [9, None, None], [20, [15, None, None], [7, None, None]]]`.
**Example:** the tree above -> `[[3], [9, 20], [15, 7]]`.
Target complexity: O(N) time and space.