How to make tea essential 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.).