These two words are a perfect illustration how important correct pronunciation is. Many students of English find it difficult to pronounce the sound /θ/properly and give up trying. They end up pronouncing /θ/ and /t/ in exactly the same way and since these two sounds are distinguishing phonemes in many English words (which means that this sound is the only sound in the word which makes the difference between the two words and gives a different meaning), this can create a lot of confusion.
So, please give correct pronunciation another chance :-)
THREE /θriː/ vs. TREE /triː/
The sound /θ/ is usually represented in the combination of letters th, while /t/ is represented as letter t.