Newly planted trees should be watered three to four times a week depending on the rain. You don't show a picture, but from your description, you are overwatering the tree. Also, is it planted correctly? The root ball should be an inch or two above the existing ground level. If the tree came out of a large nursery can it probably does not need fertilizer until the late fall. If it was field grown - it arrived wrapped in burlap - you should fertilize it in a few weeks.

Thank you. I checked the depth of the tree and it looks like what you described. Here are a couple pictures I just took.

Cut back on your watering.

This is what I learned when I worked at Duke Garden center. Water newly planted shrubs 3x a week for 2 weeks, then 2x a week for two weeks, then 1x a week for two weeks, then once a week thereafter for every week there isn't an inch of rain. Cassias always wilt when you transplant them. They don't like to be moved much. Mine lost absolutely ever single leaf when I moved it, but they came back out.

How are you watering it? Do you have a dam up around it? Are you doing a slow-watering or a fast-watering? Dig down into the ground and see how far down it is wet. If it's dry way down, try this: turn your hose on a trickle and let it just run on the roots for an hour or two. That way, the water isn't running off of the soil, but seeping down into it.

Plus, you can use a surfactant, i.e. squeeze some dishwashing liquid on top of the soil and then water. The soap makes the water "stick" to the soil.

When I transplant a shrub/tree, I do this:

Dig the hole twice as wide as the container

Fill it with water three times and let it soak into the ground

Put the shrub/tree into the hole and fill with water again and add the soil in as the water soaks in. That way, the soil gets up into the nooks and crannies of the root ball and leaves no air pockets. Speaking of air pockets, did you poke the holes for air pockets when you planted it? I'm sure you probably did.

After all this soaking and planting, sprinkle a cup of epsom salts on top around the shrub/tree and water lightly to get that soaked in.

This method has never failed me. A PITA for sure, but I've never had a plant fail if I planted it this way.

I usually leave a hose trickling @ the base of all my newly planted trees & large shrubs for a couple of days. I also fill the planting hole w/ water twice - letting it drain, then filling again before placing the tree in it.

Yes, it's important to have the surrounding soil wet, or it will just suck all the moisture out of the rootball.