Here's how you can prepare a 2% v/v tea tree oil solution.
I assume that you want to know how to prepare a 2% solution of tea tree oil.
Since you're dealing with two liquids, it's easier to go for a 2% volume by volume, v/v, percent concentration.
This means that a 2% v/v tea tree oil solution will have 2 mL of tea treee oil for every 100 mL of solution.
To make one liter of this solution, which is equivalent to 1000 mL, you'll need
So, take 20 mL of pure tea tree oil and add enough water to get the total volume of the solution to one liter.
Keep in mind that water and oil don't mix, so your solution will be layered, meaning that the tea tree oil will float on the surface of the water.
Oil and water form an emulsion, which is a solution that contains two or more immiscible liquids.
Therefore, make sure that you shake the bottle really well before using this solution.