diff --git a/src/hashtree.py b/src/hashtree.py
--- a/src/hashtree.py
+++ b/src/hashtree.py
@@ -1,4 +1,5 @@
-import hashlib
+import collections
+import hashlib
 import os
 from datetime import datetime
 
@@ -85,3 +86,19 @@ class HashTree:
 			self.store[i]=hashBlock(self.store[i*2+1]+self.store[i*2+2])
 			progress.p(i)
 		progress.done()
+
+	## Update faster than repeated insertLeaf.
+	def batchUpdate(self,keysHashes):
+		queue=collections.deque()
+		for (k,v) in sorted(keysHashes):
+			self.store[k]=v
+			parentK=(k-1)//2
+			if len(queue)==0 or queue[-1]!=parentK:
+				queue.append(parentK)
+
+		while len(queue)>0:
+			k=queue.pop()
+			self.store[k]=hashBlock(self.store[k*2+1]+self.store[k*2+2])
+			parentK=(k-1)//2
+			if (len(queue)==0 or queue[0]!=parentK) and k!=0:
+				queue.appendleft(parentK)
diff --git a/src/netnode.py b/src/netnode.py
--- a/src/netnode.py
+++ b/src/netnode.py
@@ -49,6 +49,5 @@ class NetNode:
 
 	def _updateTree(self):
 		log.info("updating hash tree...")
-		for (k,v) in self._newLeaves.items():
-			self._tree.updateLeaf(k, v)
+		self._tree.batchUpdate(self._newLeaves.items())
 		self._tree.save(self._treeFile)
diff --git a/src/tests/__init__.py b/src/tests/__init__.py
--- a/src/tests/__init__.py
+++ b/src/tests/__init__.py
@@ -0,0 +1,15 @@
+import sys
+
+
+class RedirectedOutput():
+	_stdout=None
+
+	@classmethod
+	def setUpClass(cls):
+		cls._stdout=sys.stdout
+		sys.stdout=open("/tmp/morevna-stdout.log",mode="a")
+
+	@classmethod
+	def tearDownClass(cls):
+		sys.stdout.close()
+		sys.stdout=cls._stdout
diff --git a/src/tests/test_hashtree.py b/src/tests/test_hashtree.py
new file mode 100644
--- /dev/null
+++ b/src/tests/test_hashtree.py
@@ -0,0 +1,31 @@
+import random
+from unittest import TestCase
+
+from hashtree import HashTree
+from . import RedirectedOutput
+
+
+random.seed(17)
+
+
+def buildTree(leaves):
+	tree=HashTree(len(leaves))
+	for l in leaves:
+		tree.insertLeaf(l)
+	tree.buildTree()
+	return tree
+
+
+class TestMorevna(RedirectedOutput,TestCase):
+	def test_batchUpdate(self):
+		leaves=[b"a" for i in range(8)]
+		t1=buildTree(leaves)
+		keys=list(range(8))
+
+		for i in range(8):
+			random.shuffle(keys)
+			for k in keys[:i+1]:
+				leaves[k]=bytes([random.randrange(256)])
+			t2=buildTree(leaves)
+			t1.batchUpdate((k+t1.leafStart,leaves[k]) for k in keys[:i+1])
+			self.assertEqual(t1.store,t2.store)
diff --git a/src/tests/test_overall.py b/src/tests/test_overall.py
--- a/src/tests/test_overall.py
+++ b/src/tests/test_overall.py
@@ -10,6 +10,7 @@ import config
 from hashtree import HashTree
 from client import Client, Connection as ClientConnection
 from server import Miniserver
+from . import RedirectedOutput
 
 
 config.logger.removeHandler(config.handler)
@@ -31,23 +32,17 @@ def compareFiles(f1,f2):
 	return (h,h2)
 
 
-class TestMorevna(TestCase):
+class TestMorevna(RedirectedOutput,TestCase):
 	_stdout=None
 
-	@classmethod
-	def setUpClass(cls):
-		cls._stdout=sys.stdout
-		sys.stdout=open("/tmp/morevna-stdout.log",mode="a")
-
 	def setUp(self):
 		src=os.path.join(dataDir,"test1.img")
 		shutil.copyfile(src,filename)
 
 	@classmethod
 	def tearDownClass(cls):
+		super().tearDownClass()
 		os.remove(filename)
-		sys.stdout.close()
-		sys.stdout=cls._stdout
 
 	def test_build(self):
 		treeFile=os.path.join(dataDir,"test.bin")