Treasure is usually associated with riches — gold, jewels, doubloons — the stuff contained in pirates' treasure chests. However, you can also treasure things with purely sentimental value — like your pet rock or your blankie.
The English word treasure comes from the Old French tresor, both meaning "something of great worth." Still, the French tresor sounds so much more luxurious than the English treasure, and that form is the chosen name for an expensive perfume. Worth is relative, though. Going back further, we find that the Latin word for treasury is thesaurus, which is what a book of synonyms is called. Guess the ancients always understood the richness — and worth — of words.