Not able to view the side view of its stem, I could only speculating for you. It looks like a type of vine, perhaps jungle grape/water vine (Cissus hypoglauca). Check it out and see if you have a match. When it blooms and you still don’t know, make new post with flower’s photo. For now check out the link below for more information, Best wishes! https://www.google.com/search?q=cissus+hypoglauca&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjW_sSAzdfTAhXqrlQKHf3pDpcQiR4IgAE&biw=1879&bih=908#imgrc=tLM06_fEMaFHPM: