Call BeginUpdate before making several changes to the nodes in the list (such as adding or removing several nodes). BeginUpdate increments the UpdateCount property, to keep track of the fact that the list is in the middle of an update. When the update is complete, call EndUpdate to decrement the UpdateCount property.  

Every call to BeginUpdate should be matched by a call to EndUpdate, so that the UpdateCount property accurately reflects whether an update operation is underway. 

UpdateCount 

EndUpdate