Binary Tree in Clojure. Comments on how to improve the code are welcome. It feels like it's somewhat repetitive, and maybe not fully idiomatic Clojure?

core.clj

(ns test-bench.core)

(defprotocol BinaryTree
  (member? [_ e] "Check if e is a member of the BinaryTree")
  (insert [_ e] "Insert an element in the tree")
  (delete [_ e] "Remove element from tree"))

;; Need to forward declare factory functions.
(declare leaf node delete)

;; A leaf is an empty node in the tree.
(defn leaf [] (->Leaf))
(defrecord Leaf []
  BinaryTree
  (member? [this e] false)
  (insert [this e] (node e))
  (delete [this e] this))

;; A node have an active value and a left/right node.
(defn node
  ([v] (node v (leaf) (leaf)))
  ([v l r] (->Node v l r)))
(defrecord Node [value left right]
  BinaryTree
  (member? [this e]
    (if (= value e) true
        (if (> e value)
          (member? right e)
          (member? left e))))
  (insert [this e]
    (if (= value e) this
        (if (> e value)
          (node value left (insert right e))
          (node value (insert left e) right))))
  (delete [this e]
    (if (= e value) (removed value left right)
        (if (> e value)
          (node value left (delete right e))
          (node value (delete left e) right)))))

;; A removed node is a place-holder for a removed element.
(defn removed [e l r] (->RemovedNode e l r))
(defrecord RemovedNode [value left right]
  BinaryTree
  (member? [this e]
    (if (= e value) false
        (if (> e value)
          (member? right e)
          (member? left e))))
  (insert [this e]
    (if (= e value) (node value left right)
        (if (> e value)
          (delete value left (insert right e))
          (delete value (insert left e) right))))
  (delete [this e]
    (if (= e value) this
        (if (> e value)
          (node value left (delete right e))
          (node value (delete left e) right)))))