How to make tea essential oil? I tried to make my own tea essentials oil by putting small pieces of tea leaves (dehydrated) into my local alcohol (29% vol).

After 1 week, the leaves turned brown, so I removed them out of the bottle. Now the remaining looks dark, strong smell of tea and alcohol.

I wonder if it can be called tea tree essential oil and can be used in beauty products like body wash or even in food?

This is my first time I've tried to make essential oil, so not sure what to do properly as there's no direct instruction on google that show how to make tea oil.
You have basically made tea-flavoured vodka. 

The tea tree (for essential oil) is unrelated to the tea plant for the beverage.

Commercially, tea tree oil is produced by steam distillation of the leaves of the tea tree, specifically Melaleuca alternifolia. Though possible to obtain leaves and perform the distillation, it's probably not practical on a small scale outside of the tea tree production regions. For completeness, tea tree oil is toxic; you don't want to eat it.

What you used was conventional tea leaves. The tea beverage is made by steeping (soaking in hot water) leaves of the tea plant, which have been dried or otherwise prepared (e.g., fermented, roasted, etc.).