merkle_tree:insert_node/4: is an element is already in the list, keep the current node
merkle_tree:insert_node/4: is an element is already in the list, keep the current node

also: after inserting something, make the hash invalid (just in case)
jvf/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris,scalaris-team/scalaris,jvf/scalaris,caijieming-baidu/scalaris,jvf/scalaris,caijieming-baidu/scalaris,scalaris-team/scalaris,jvf/scalaris,caijieming-baidu/scalaris,jvf/scalaris,jvf/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris,jvf/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris,scalaris-team/scalaris,caijieming-baidu/scalaris