Q.bringing our ficus tree inside after being outside all summer
Do I need to treat the soil for insects, etc. before bringing it in?

Before any plant is brought in for the winter, there are several steps to take. The first and most important is to acclimate the plant gradually to lowered light. This is an ongoing process, so a few days before you start bringing it in, you'll want to flood the soil with water a couple of times, to make sure any ants, worms, etc exit outdoors. You will also want to inspect the plant for bugs, especially the undersides of leaves and branches, and the leaf axils ( where leaf stem emerges for main stem.) Spray all these surfaces with a mild soap solution, add a little neem oil if you want, to make sure the invisible bugs are given their walking papers also. This article has more information: https://www.gardeningknowhow.com/houseplants/hpgen/acclimate-plants-indoors-winter.htm