J Maple from 2013 - 2016

I bought this Japanese Maple from Brent in June of 2013. Trunk about 5/8" in diameter, healthy.  
When I got it, I planted in a small area with other Bonsai-to-be trees.



This year, we were having a very early warm spell, so I dug it up on 2-28-16 and potted it.
It now stands 32" tall, 24" wide and the trunk is 1 1/2" in diameter.




My only concern is the big weird root it has developed. Any ideas what I can do with it?
Thanks for all of the help I get from everybody!!! 

BTW.... The Maple is supposed to be 18 years old now.

I agree that root needs some attention.

I would start with a very tight wire tourniquet of about 3 or 4 strands of 2 or 3mm aluminium wire around the part just behind the swelling.

Bury it a bit deeper in the ground and hopefully the tourniquet will cause it to put out roots so that you can chop off the swelling.

Thanks for the info, I'll see what I can do!