Q.two holly trees are not showing dense growth
I have two holly trees that are 10 years old, both are not dense in growth. Good green color and berries but not dense growth. How can I improve growth density?

Though your Holly looks lovely, I do see that it appears thinned out.
I would start with basics. Growing conditions, proper full sunlight and soil condition.
A simple soil test takes the guesswork out of what it may need.
A regular fertilizer schedule will help your plant.
Then pruning! Read the links below to refresh you on the care requirements and to help you get started.
https://www.gardeningknowhow.com/ornamental/shrubs/holly/common-types-of-holly.htm
https://www.gardeningknowhow.com/ornamental/shrubs/holly/growing-holly-bushes.htm
https://www.gardeningknowhow.com/ornamental/shrubs/holly/trimming-holly-bushes-how-to-prune-holly-bushes.htm
https://www.gardeningknowhow.com/ornamental/shrubs/holly/fertilizing-holly-bushes.htm