diff --git a/src/hashtree.py b/src/hashtree.py
--- a/src/hashtree.py
+++ b/src/hashtree.py
@@ -13,8 +13,8 @@ class HashTree:
 	def __init__(self,leafCount):
 		self.store=[b""]*(leafCount*2-1)
 		self.leafStart=leafCount-1
-		self.index=self.leafStart
 		self.leafCount=leafCount
+		self._index=self.leafStart
 		
 	@classmethod
 	def fromFile(cls,filename):
@@ -52,14 +52,13 @@ class HashTree:
 		with open(filename,"wb") as f:
 			for h in self.store:
 				f.write(h)
-
 		
 	## Inserts a leaf at the first empty position.
-	#	
+	#
 	#	Useful and used only during the tree construction.
 	def insertLeaf(self,h):
-		self.store[self.index]=h
-		self.index+=1
+		self.store[self._index]=h
+		self._index+=1
 		
 	## Updates a hash stored in the leaf.
 	def updateLeaf(self,index,h):