What do I need to do for a gold laurel wreath?

I do not know for sure, but for every one of mine that's gold I have gathered every treasure in that chapter.

Yah the wreaths represent if you've opened every treasure chest, gone through all intensity gates, and found every zodiac item. Only then will the wreath be gold.

It is in fact collecting every item in the level. This also makes the percentage for your file go up. At least one level requires a difficulty of 9.0, so this is not an easy feat for every level. Good luck to you and your quest for golden wreaths. I wish everyone luck including myself on that haha.