Certified GKH Gardening Expert
When you get blossoms but no fruit, or when blossoms drop, this is normally an indication of poor pollination. If there are not enough natural pollinators around or if it's grown indoors, the tree will have difficulty producing. This is why we sometimes have to intervene by hand pollinating. Just use a small paint brush and swirl it around the inside of the flower and repeat on all the flowers on the plant.
You can encourage additional pollinators to the area for outoor trees. Here is more information on that: https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm