Islamic advice

Hello!! I am international student in London. My dad sends me money every month for food travel and other daily expenses. I have been wanting to get a skin treatment for so long so I saved half of the money my dad sends me so that I can get this treatment done. But ofc my parents won’t know about this.

Is it Al right ? I mean to spend money on a different purpose without my parents permission? I won’t ask them for extra money it’s just that I spent very less on daily expenses and saved as much as I could. But is it okay to spend this saved amount on something other than daily expenses!!!

I’m asking this specifically in Islamic point of view, thanks