Help with essential oils in shampoo

So I just used that desert essence organics tea tree lemon an it worked great except I still have dandruff so is there a way I can add certain essential oils to the actually shampoo so the dandruff goes away? And if so wat oils r best and how much?
updated by @zack4: 01/13/15 09:02:42PM

Diluted vodka? Can u explain why n how cuz ive never heard of doin that before

rosemary is best pepermints good

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My new book Ban The Taboo Vol 1

Thhanks elizabeth ill try that next time I wash