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Without knowing what kind of tree, how big, where, what are the growing conditions and maintenance practices, I could only guess. Here are some possibilities. In evergreens, the problem is usually ongoing for up to a year before symptoms show. You may want to call your local extension agent for help and to assist with a soil sample.

https://www.gardeningknowhow.com/ornamental/trees/pine/pine-tree-drying-bottom.htm

https://www.gardeningknowhow.com/ornamental/trees/tgen/dry-brittle-tree-branches.htm

https://www.gardeningknowhow.com/ornamental/trees/pine/pine-tree-browning.htm

Usually, with evergreens such as this kind, you won't see needle recovery. Any damage will affect the look permanently. They will put new growth, usually, only on the top and tips of existing branches.

Depending on the exact species, some sprout new trees at the base which can replace the existing tree once cut down. Some species will die completely if you cut them back like this, so it will be important to know exactly what the tree is.

Unfortunately, it may have been watered a little too regularly. Overwatering is the most common cause for needles or scales turning brown. Cold is another cause, but this will, clearly, not be the case here.

It is best to only water once the soil is dry down to about 4 inches or so. These trees are quite drought tolerant, and will not need extra water unless there is drought. Even then, it is best to allow the soil to dry out down to that depth before watering again.

From here, you will want to cut off the browning portions, as they will not return to normal. Treat with a fungicide as well. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

I would also treat with about 1/2 cup of DOLOMITIC LIME and a tablespoon of WETTABLE SULFUR. This can help to remedy the situation and bring the soil back to a more suitable condition.

Here is an article that will help you to treat this infection:

https://www.gardeningknowhow.com/plant-problems/disease/learn-about-plant-rust-disease-and-rust-treatment.htm

An expert would want to closely inspect the bark, cones and needles to identify your tree. We suggest you contact your County Extension office for help with this. This may be your local office's website: https://extension.psu.edu/bucks-county.

If you decide to trim the bottom of the tree, it should be done when the tree is not actively growing, in late winter or early spring.

You may enjoy this article: https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-7/zone-7-evergreen-trees.htm

You are in either growing zones 5 or 6.
These articles will help you.
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-5/zone-5-evergreen-trees.htm
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-6/evergreen-trees-for-zone-6.htm

Also visit your local garden centers; they often have display gardens to help you make landscape decisions.