breadth-first search is annoying in Clojure

bfs.clj

;; https://stackoverflow.com/questions/11409140/stumped-with-functional-breadth-first-tree-traversal-in-clojure

(def tree [1 [2 [4] [5]] [3 [6]]])

(defn bfs
  [tree]
  (loop [ret []
         queue (conj [] tree)]
    (if (seq queue)
      (let [[node & children] (first queue)]
        (println queue)
        (println ret)
        (recur (conj ret node)
               (into children (next queue))))
      ret)))