Hi,
My first thought is not enough light or heat.
What you are calling "sub branches" are actually leaves. They have compoiund leaves about a foot long, with leaflets arranged down the sides. So it is normal to drop the whole leaf (what appears to be an entire branch). It is scraggly in its growth, which probably means not nearly enough light. What strength of light do you have on it and for how long? You dont really need a plant light, just MORE light. Lots more light. For my full sun trees in my greenhouse, I may have four, 4 ft, 2 bulb LED or fluorescent lights, kept about a foot above the top of the tree. And thats in a greenhouse, not in a house window.
They also like lots of heat. If it is outdoors in summer and your nighttime temps drop to in the 50s or 60s, it will be hard to get good growth.
You can get a phone app called Photone that measures your current light and tells you how much light it is getting (in PPFD and DLI. Lumen measurements are fairly useless for plants). Virtually no light that is useable by plants gets through a glass window. Visible light, yes, but not what plants need.
From experience, it is really hard to grow full sun trees indoors.
Where in Oregon are you? Build a greenhouse! It's lots of fun

Cheers,
Carolyn (Boise Idaho)