Make definition of Tree private

src/SplayHeap.agda

@@ -24,7 +24,8 @@ open import Relation.Binary.PropositionalEquality using (_≡_; refl; cong; modu
 open import Relation.Nullary.Construct.Add.Extrema
 open import Relation.Nullary.Decidable.Core
 
-data Tree (l u : Carrier ±) : Set (c ⊔ ℓ₂) where
+private
+  data Tree (l u : Carrier ±) : Set (c ⊔ ℓ₂) where
     leaf : .(l ≤± u) → Tree l u
     node : (x : Carrier) → Tree l [ x ] → Tree [ x ] u → Tree l u