fix: implement Ord for BranchKey

Author: TheWaWaR

src/tree.rs

@@ -6,6 +6,7 @@ use crate::{
     vec::Vec,
     H256, MAX_STACK_SIZE,
 };
+use core::cmp::Ordering;
 use core::marker::PhantomData;
 
 /// The branch key
@@ -21,6 +22,20 @@ impl BranchKey {
     }
 }
 
+impl PartialOrd for BranchKey {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+impl Ord for BranchKey {
+    fn cmp(&self, other: &Self) -> Ordering {
+        match self.height.cmp(&other.height) {
+            Ordering::Equal => self.node_key.cmp(&other.node_key),
+            ordering => ordering,
+        }
+    }
+}
+
 /// A branch in the SMT
 #[derive(Debug, Eq, PartialEq, Clone)]
 pub struct BranchNode {