Q.Care for a ficus tree
This plant was in bright light and same location for years. Drops leaves and is all stem to the very top where there are some leaves on 5 or 6 branches.
Ficus trees that have plenty of light, yet lose leaves, often green ones, steadily month after month (or year after year) are usually suffering from chronic overwatering. That is, the soil never has a chance to dry (or aerate,) sufficiently near the bottom of the pot. The moisture builds up there over time, gradually killing the roots (which need to have air around them so they can breathe.) Less roots mean less water is taken up, which means - if you are adding the same amount of water all the time - that even more moisture accumulates, killing roots higher and higher from the bottom of the pot. Eventually, you only have roots in the top few inches of the pot, everything below them having become an airless swamp.
However, ficus are among the toughest plants we use, and you can save yours if you can do a few simple things. The first is to learn how to test the soil moisture ALL THE WAY TO THE BOTTOM OF THE POT. You can use a moisture meter, or a simple bamboo skewer or thin wooden dowel, which you can stick into the soil, all the way to the bottom, then pull it up and feel it. When it's time to water, the wood will feel only lightly damp, or the meter will show about 3/4 if the way between dry and moist. This article tells you more about that: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
After you've acquired something to test the moisture, you need to get your ficus out of all that wet. Pull it out of the pot, discard old soil, cut off brown, dead, and/or mushy roots, and repot. You may need to put it into a smaller pot, if its lost a lot of roots. Make sure to put the new potting mix under the root ball, so the top of the soil is at the same level as it was previously. (Putting new soil on top of the root ball will smother the roots.) Use a new potting mix with very good drainage - I like cactus potting soil mixed 50/50 with perlite. Here's an article with tips on dealing with root rot in houseplants: https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm
You'll also need to cut back some of those leafless branches; you can probably cut them back by 1/2 - 2/3, but not all at once - you need some leaves on the tree to produce energy. As the pruned branches start to sprout leaves, you can cut back the longer ones. Here's another article that has more tips: https://www.gardeningknowhow.com/houseplants/ficus/ficus-losing-leaves.htm