I personally, in my own sensibilities do not like most exposed roots. Horticulturally, the roots you have exposed on your Nashia probably won't survive long term. The Nashia is in the Verbena family, and is more a woody herb than a true wood forming tree. Those exposed roots will likely dry out, and die off. If it were on my bench, I would repot it right now and bury all the roots by at least 1/4 inch. You can expose roots later, when the tree is older, and the trunk is greater than one inch (2.5 cm) in diameter. When you repot lower you can slant the trunk right or left to give it some movement. This species of tree is most often is styled by ''clip and grow'', by letting it grow out, then once or twice a year cutting back to just a few leaves per branch. Once a twig is over a year or so old, they are very brittle, which is why clip and grow is the usual choice. If it were mine, I would identify the main trunk line, and prune so all branches are very short. Then I would let it grow out for one or two years, without pruning. Then prune back hard. The growing out is what will thicken up your trunk. Nashia can become a shrub 6 of more feet tall (over 2 meters). It grows in the Bahamas, on coral derived soils. Because of goats foraging, the ''wild population'' of Nashia has at one point been reduced to just 4 bushes documented as truly wild, having not been planted by man. However, in the Bahamas it is very common in the back yards of locals. A popular landscape or garden shrub.
The Operculicarya decaryi is an interesting pachycaul from Madagascar. It comes from a Monsoon desert. Warm to hot temperatures with lots of water or slightly cooler warm to hot with cooler nights full sun and absolutely zero rain for months on end. Like the baobab it has a spongy layer of tissue under the bark that is a water storing layer. This tissue layer can give the tree a lumpy look, No matter what you do you will have areas that look like reverse taper as parts of the trunk will swell, and other parts will not. Don't worry about it, it is the nature of the tree and if any tell you you have to chop it here or there to get rid of the reverse taper, ignore them. Because no matter what you do this species will have zones of swelling, and will always, always have areas that look like reverse taper. Embrace the look and go with it.
One advantage of Operculicarya is that you can summer it outdoors, full sun and frequent water. Then as cooler weather approaches let it dry out. Let it get bone dry. Then set it on a shelf for the winter. As long as it is above freezing and bone dry the tree will sit dormant until the ''rains return''. Space indoors at my house is limited in winter. I would just set my Operculicarya on a windowsill and not water it again until spring. 5 months with no water was no problem. Gave it to my then high school age nephew, sometime during his many moves from dorm to apartment to another apartment during college year he lost it. I should get another one. I thought it fun.
Operculicarya is an opportunistic grower, it does not have to have a dry monsoon rest period. As long as it is sunny, wet and warm, it will keep growing. It does not require a dry rest to ''set buds for new growth''. So if you keep it growing year round it will be happy. And if you decide the ''dry rest'' should come in summer while you are on vacation, no problem.