Cupressus x leylandii, AKA Leyland Cypress and until recent years it was × Cuprocyparis leylandii. New genetic research has found that one it's parents was misnamed, resulting it being given a new botanical name as well.
The Leyland Cypress is a fast vertical growing tree, growing on average 3' a year. I have personally have had landscapers report it growing as much as 5' in one year. This trait has lead it to become a popular hedge/screening tree.
This tree is grown only from cuttings. If left to grow naturally the start as very tall skinny trees filling out with age. Some growers, like the large US grower Monrovia, shear these trees when they are young. Which results in a fuller denser looking tree, but this means it takes the grower longer to get to the same height, as the first grower that left it to grow natural.
If you had received the fuller denser tree and did not know you needed to shear it once a year and shape it throughout the year, your tree would soon be spares above the growers work.
How do you get a fuller denser tree start with pruning in the summer. Winter pruning promotes fast growth in a tree, where summer pruning and shearing promotes dense growth. If you want a tree that continues to get tall, but remains fuller, in early summer remove 2/3 of this springs' top growth and shape the side shoots, shearing them back some. The tree will continue to grow through out the rest of the summer. Each year at early summer you will repeat this routine. Never removing any of the summers growth, just 2/3 of the Spring's growth. If you want to control the size of your tree you will want to prune all of this summers growth and then again in early-autumn prune the summers growth. Making sure you do so early not too late in the year. Winter pruning will promote fast growth in spring. The opposite of what you are trying to achieve. Royal Horticultural Society recommends pruning this tree 2-3 times
You can always leave the tree to grow as it would naturally resulting in a 50' or more tree.
Plant Leyland Cypress in a full sun location. In well drained soil. This tree is quite drought tolerant, the opposite of most hedging trees, which require quite a bit of irrigation. Missouri Botanical Garden information on Leyland Cypress