Is it a decidious oak, if so it will naturally lose its leaves. Even in a pot it will need to grow outside all year, ther is no such thing as an indoor tree. Have you ever seen a tree grow naturally indoors.
Trees growing in pots tend to be less vigourous than trees growing in the ground and will require some sort of protection from the elements, some shade in the summer, frost and wind protection in tthe winter, there is no need to protect from snow as it insulates from other extremes.
Try a good book on bonsai, anything by Peter Adams, his books are readilly avaiilable and should give enough tips. He now, I believe , lives in the USA and has a good following.
Alternatively see some of my bonsai hubs or the others on site to find some help.