Just googled where sesame seeds come from (it never occurred to me to ask before) and found that they grow in pods that are hung upside down to ripen until they burst open and release their seeds. The treasure is revealed.
The alternate theory is that "sesame" was a bastardized form of the Talmud, šem-šāmayīm, or "in the name of heaven".
But what I find most intriguing is the likelihood that the phrase was a play on words referring to both. Oil has been seen as godly since time immemorial, sesame is the oldest oil crop to humanity. It's why sesame was seen as treasure at all. Even the word anoint just means to mark with oil, and think of how we use that word.
