Code wars "Sort binary tree by levels"

sort_tree.rb

# return the array containing the tree levels, from root to last level.
def tree_by_levels(node)
  return [] unless node
  result = []
  q = [node]
  until q.empty?
    node = q.shift
    q << node.left if node.left
    q << node.right if node.right
    result << node.value
  end
  result
end

thanks