Maybe it needs more root space, or a different type of soil that will retain moisture better. A tree can be given plenty of water and be in a humid environment, but if the root system is not adequately established the plant will still have difficulty and the leaves can dry out.

I just repot into a bigger pot not too long go. Do wax Apple tree require a lot of waters? What kind of fertilizer should I use for it?

All of the leaves on mine fell off and it hasn't regrown anymore at all since winter, I wish I could help..