diff --git a/src/client.py b/src/client.py
--- a/src/client.py
+++ b/src/client.py
@@ -151,6 +151,7 @@ class Client(NetNode):
 		print(datetime.now(), "receiving data:")
 		progress = Progress(len(blocks_to_transfer))
 
+		last_flushed = datetime.now().timestamp()
 		for k in range(0, len(blocks_to_transfer), conf.batch_size.data):
 			indices = blocks_to_transfer[k:k+conf.batch_size.data]
 			self._outcoming.write_msg({"command": "req", "index": indices, "dataType": "data"})
@@ -160,10 +161,14 @@ class Client(NetNode):
 				block = bin_data[j*HashTree.BLOCK_SIZE:(j+1)*HashTree.BLOCK_SIZE]
 				data_file.write_at(i, block)
 
+				log.info("block #{0}: {1}...{2}".format(i, block[:5], block[-5:]))
 				if self._tree_file:
 					self._new_leaves[i+self._tree.leaf_start] = hash_block(block)
 
-				log.info("block #{0}: {1}...{2}".format(i, block[:5], block[-5:]))
+					t = datetime.now().timestamp()
+					if t-last_flushed >= 60 and self._tree_file:
+						self._update_tree()
+						last_flushed = t
 
 				stats.log_transferred_block()
 				progress.p(k+j)
diff --git a/src/netnode.py b/src/netnode.py
--- a/src/netnode.py
+++ b/src/netnode.py
@@ -71,4 +71,5 @@ class NetNode:
 		log.info("updating hash tree...")
 		self._tree.batch_update(self._new_leaves.items())
 		self._tree.save(self._tree_file)
+		self._new_leaves = dict()
 		log.info("tree updated")
diff --git a/src/server.py b/src/server.py
--- a/src/server.py
+++ b/src/server.py
@@ -1,4 +1,5 @@
-import socket
+from datetime import datetime
+import socket
 import ssl
 import multiprocessing
 import logging as log
@@ -62,6 +63,7 @@ class Server(NetNode):
 		self.BLOCK_SIZE = self._tree.BLOCK_SIZE
 
 		self._data_file_obj = None
+		self._last_flushed = 0
 
 	@staticmethod
 	def run(connection, *args):
@@ -94,6 +96,7 @@ class Server(NetNode):
 			if json_data["action"]=="push" and not self.is_locked():
 				self._lock()
 
+			self._last_flushed = datetime.now().timestamp()
 			self._outcoming.write_msg({"command": "init", "version": conf.version})
 
 		elif json_data["command"]=="req":
@@ -146,6 +149,11 @@ class Server(NetNode):
 			if self._tree_file:
 				self._new_leaves[k+self._tree.leaf_start] = hash_block(block)
 
+		t = datetime.now().timestamp()
+		if t-self._last_flushed>=60 and self._tree_file:
+			self._update_tree()
+			self._last_flushed = t
+
 		return ({"command": "ack", "index": indices},)
 
 	def _finalize(self):