Redwood Ryan
Masterpiece
Are you absolutely positive?
I picked up a book by Peter Warren called Bonsai. In the book it has a section on deciduous trees and lists the Chinese Elm as a very tough deciduous bonsai that can be grown indoor or out, that it is tolerant of a wide range of climates and that it needs plenty of sun which the window where I would put it has a lux measurement that goes beyond my phone's meter limit of 10,000 lux.
Trust me, many, many people like you come to the forum with the plans on growing an outdoor tree indoors. It won't last long, trust me when I say that. A window would not be anywhere near sufficient enough to keep it happy. A lot of people will say that elms can be grown indoors, but don't mention long-term health. The trees eventually tire of non-stop growing and die.
Believe me when I say this, I'm an indoor grower of Ficus with lots and lots invested to keep my trees happy.