TIA

The picture of whole tree

I don't understand. Are you upset because trunks are brown? If so, don't be. Pachira trunks brown w/age. Your tree is large, so a brown trunk is normal.

Leave falling. There are several reasons leaves brown/yellow and fall off.

Don't want to sound like the voice of doom, but have you checked for insects? Sticky leaves, white or brown bumps, webs or spots that shouldn't be on leaves/stems?

During winter, Pachira soil should dry between watering.
I grow my two as succulents.
By chance, are you over-watering? Also, is soil well-draining?

Years ago, whenever I purchased Pachiras, they died.

Deciding to try once again, I purchased Pachira from a nursery that sells succulents, fat plants and bulbs. 1990.
Instead of caring for new Pachira as I did ex-Pachiras, 'as tropicals,' 'after reading the care sheet included w/plant,' I decided to grow Pachira as a succulent.

Pachira was potted in a very small container, 3", (Pachira was a stick that arrived bare-root,) bright light, outdoors during summer, no direct, summer sun, and under-potted. It worked...it's alive and healthy.

I bought a braided Pachira which is cared for the same way. No shedding on either plant.

So, despite medium your Pachira is potted in, allow soil to dry, 'almost' completely. As you would a succulent.

Good luck, Toni

This is fairly common with braided Pachira. I usually tell folks to select the healthiest trunk,
and then separate and re-pot it as a solo plant. It is possible to keep braided Pachira healthy,
but I've seen so many simply die back to one trunk that I like to mention it right up front.

With that green growth on the dying trunk, you can actually cut the still-vital tip
and attempt to root it. Not the best time of year for it, but what can it hurt, right?

If it's any consolation, the rot had probably set in when the plant was still at Lowe's. Even
a re-potting at the time of purchase might not have saved that trunk. Clearly, something needs
to be done, though, before the remaining trunks suffer a similar decline.

Josh

No there is no insects, I am quite sure. Also I do not believe it is over watering - I have it 2 months and only watered once.

Josh, So you think I should repot it into a gritty mix now (instead wait until spring?) There is no way to save that rotting trunk? I kind like 5 trees together (even they are not braided) as I do not have that many pots and places to put them.

If you've only watered once in two months, I must assume that the soil holds too much moisture....
otherwise, you've been underwatering. I've watered my Pachira twice in the past two weeks,
especially since there are new leaves growing.

I always hesitate to suggest an out-of-season re-potting, but if it means the difference between
the life and death of a plant....well, the choice is obvious.

Josh