One way

?node_id=3989;BIT=%20Trie%20;BIS=%27

Surround it with spaces but change the string separator to something different than spaces.

I chose a single quote ' here as separator but anything different goes, even XXX

?node_id=3989;BIT=%20Trie%20;BIS=XXX

Update

NB any instance of "trie" surrounded by anything else than spaces, like punctuation would be missed though.

Like trie! at the end of a phrase.

Another thing is to add the substrings you don't consider hits to the "skip text" and "skip titles" fields:

?node_id=3989;BIT=Trie;BET=tries%20tried%20triev;HET=tries%20tried%20triev

Of course, that isn't perfect either, especially if "tries" - plural of "trie" - shouldn't be excluded.

By default, Super Search searches for substrings as well. There is no easy way to search for exact words without searching for substrings. You can do so by using an alternate search term separator and then searching for trie_ (blank replaced by underscore here for emphass), but that will again miss stuff in your node, like "trie".

?node_id=3989;BIT=trie%20;BIS=%20-

:P https://www.google.com/search?client=firefox-b-1-d&q=site%3Aperlmonks.org+%22trie%22

Your welcome! :(