-- this will be the complicated case
insertNode contextNode@TrieNode{children=childNodes,nodeType=oldNodeType}
           SharedPrefixDatum { shared = sharedPrefix ,
                               suffixS = sourceSuffix@(s:ss),
                               suffixT = targetSuffix@(t:ts)}
               = newForkNode {children = ourTwoNewNodes }
    where newForkNode = nonWordNode sharedPrefix
          ourTwoNewNodes = Map.fromList [(s,newSourceSuffixNode),(t,newTargetSuffixNode) ]
          newSourceSuffixNode = wordNode sourceSuffix
          newTargetSuffixNode = contextNode{ wordFragment = targetSuffix}