Keep outside in a sheltered position.
Not sure what the weather looks like .. Considering the young growth on the plant, the tree has been indoors untill now. Putting it outside right now, with freezing temperatures at night would be a sure-fire way of getting serious damage on the tree.
If you want to place the tree outdoors, make sure you give the tree a few weeks to get settled & ready for winter by slowly giving it a colder surroundings. Do you have an unheated shed with a window? If no frost occurs you could keep it there untill it is dormant.
In general plants do not like the hot feet & dry air associated with windowsill-with-heating. So indeed, that might not be the best spot. On the other hand.. I have loads of plants on windowsills with heating below. It is however a bit tricky.