diff --git a/src/database.rs b/src/database.rs
index 329940b..6b82857 100644
--- a/src/database.rs
+++ b/src/database.rs
@@ -1,5 +1,7 @@
 use crate::*;
 
+use std::collections::HashMap;
+
 /// Trait that must be implemented for a Database
 pub trait Database {
     /// Creates new instance of db
@@ -17,4 +19,7 @@ pub trait Database {
 
     /// Puts the value to the db by the key
     fn put(&mut self, key: DBKey, value: Value) -> Result<()>;
+
+    /// Batc
+    fn put_batch(&mut self, subtree: &HashMap<DBKey, Value>) -> Result<()>;
 }
diff --git a/src/hasher.rs b/src/hasher.rs
index 10a544e..3769390 100644
--- a/src/hasher.rs
+++ b/src/hasher.rs
@@ -1,9 +1,11 @@
 use crate::*;
 
+use std::fmt::Debug;
+
 /// Trait that must be implemented for Hash Function
 pub trait Hasher {
     /// Native type for the hash-function
-    type Fr: Copy + Eq + Default + Sync + Send;
+    type Fr: Copy + Eq + Default + Sync + Send + Debug;
 
     /// Serializes Self::Fr
     fn serialize(value: Self::Fr) -> Value;
diff --git a/src/tree.rs b/src/tree.rs
index 5ba94ae..772b70e 100644
--- a/src/tree.rs
+++ b/src/tree.rs
@@ -213,11 +213,23 @@ where
 
         let subtree = Arc::new(Mutex::new(subtree));
 
-        let n = rayon::ThreadPoolBuilder::new()
+        let root_val = rayon::ThreadPoolBuilder::new()
             .num_threads(8)
             .build()
             .unwrap()
-            .install(|| Self::batch_recalculate(root_key, subtree, self.depth));
+            .install(|| Self::batch_recalculate(root_key, Arc::clone(&subtree), self.depth));
+
+        let subtree = Mutex::into_inner(Arc::try_unwrap(subtree).unwrap()).unwrap();
+
+        // self.db.put_batch(&subtree.into_iter().)?;
+
+        // Update root value and next_index in memory
+        self.root = root_val;
+        self.next_index = end;
+
+        // Update next_index value in db
+        self.db
+            .put(NEXT_INDEX_KEY, self.next_index.to_be_bytes().to_vec())?;
 
         Ok(())
     }
@@ -262,20 +274,20 @@ where
         subtree: Arc<Mutex<HashMap<Key, H::Fr>>>,
         depth: usize,
     ) -> H::Fr {
-        // if key.0 == depth {
-        //     return subtree.into_inner().unwrap().get(&key).u;
-        // }
+        if key.0 == depth {
+            return *subtree.lock().unwrap().get(&key).unwrap();
+        }
 
-        // let (left, right) = rayon::join(
-        //     || Self::batch_recalculate(key, subtree, depth),
-        //     || Self::batch_recalculate(key, subtree, depth),
-        // );
+        let (left, right) = rayon::join(
+            || Self::batch_recalculate(Key(key.0 + 1, key.1 * 2), Arc::clone(&subtree), depth),
+            || Self::batch_recalculate(Key(key.0 + 1, key.1 * 2 + 1), Arc::clone(&subtree), depth),
+        );
 
-        H::default_leaf()
-    }
+        let result = H::hash(&[left, right]);
 
-    fn db_batch_insert(&mut self, subtree: HashMap<Key, H::Fr>) -> Result<()> {
-        Ok(())
+        subtree.lock().unwrap().insert(key, result);
+
+        result
     }
 
     /// Computes a Merkle proof for the leaf at the specified index
diff --git a/tests/memory_keccak.rs b/tests/memory_keccak.rs
index 9d52649..342e275 100644
--- a/tests/memory_keccak.rs
+++ b/tests/memory_keccak.rs
@@ -24,6 +24,10 @@ impl Database for MemoryDB {
 
         Ok(())
     }
+
+    fn put_batch(&mut self, subtree: &HashMap<DBKey, Value>) -> Result<()> {
+        Ok(())
+    }
 }
 
 impl Hasher for MyKeccak {
diff --git a/tests/poseidon.rs b/tests/poseidon.rs
index 977040e..cab941e 100644
--- a/tests/poseidon.rs
+++ b/tests/poseidon.rs
@@ -61,6 +61,10 @@ impl Database for MemoryDB {
 
         Ok(())
     }
+
+    fn put_batch(&mut self, subtree: &HashMap<DBKey, Value>) -> Result<()> {
+        Ok(())
+    }
 }
 
 impl Database for MySled {
@@ -95,6 +99,10 @@ impl Database for MySled {
 
         Ok(())
     }
+
+    fn put_batch(&mut self, subtree: &HashMap<DBKey, Value>) -> Result<()> {
+        Ok(())
+    }
 }
 
 #[test]
diff --git a/tests/sled_keccak.rs b/tests/sled_keccak.rs
index 21b1366..fbe49aa 100644
--- a/tests/sled_keccak.rs
+++ b/tests/sled_keccak.rs
@@ -1,5 +1,6 @@
 use hex_literal::hex;
 use pmtree::*;
+use std::collections::HashMap;
 use std::fs;
 use tiny_keccak::{Hasher as _, Keccak};
 
@@ -38,6 +39,10 @@ impl Database for MySled {
 
         Ok(())
     }
+
+    fn put_batch(&mut self, subtree: &HashMap<DBKey, Value>) -> Result<()> {
+        Ok(())
+    }
 }
 
 impl Hasher for MyKeccak {