Close up picture of the leaves on the top of the tree canopy & picture of the mulched tree trunk...

It looks like the tree is struggling to establish its root system. This pertains to site conditions, planting techniques, care of the tree after planting, overwatering or underwatering, etc. If the tree was balled and burlapped were the cords removed and burlap cut loose. If the tree was root bound within the container, were the roots teased apart so they could establish into the existing soil.  Here is our webpage on factors that contribute to decline https://extension.umd.edu/resource/what-causes-trees-die

Also, the holes in the leaves show symptoms of Japanese beetle damage. Purple leaf plum is favored by them.

We notice that the tree may be planted too deeply and there is excessive mulch around the base. Overtime root balls can settle even further into the ground. This can cause failure to establish, trunk damage, poor growth, and decline. A properly planted tree flares at the base of the trunk at the soil line where it joins the root system. In some cases, soil is piled up around trunks at the plant nursery prior to digging up the trees for shipment. https://extension.umd.edu/resource/trees-planted-too-deeply

Excess mulch - can cause bark deterioration at the soil line, roots can grow into the mulch. Light watering may only wet the mulch layer while the soil remains dry. https://extension.umd.edu/resource/excess-mulch-problems

Watering - Check the soil moisture about once a week for new plants especially during dry periods. Water deeply if needed. Move the mulch aside and check the soil moisture by probing with a screwdriver about 6 inches deep and feel with your finger. Soil should be damp too the touch. Let the soil dry before watering again. See watering guidelines https://extension.umd.edu/resource/watering-trees-and-shrubs

At this point, the tree looks like it has been planted too deeply and overmulched. Root collar excavation, which is the removal of excess soil and mulch around the root collar(base of the tree) can be helpful. Carefully remove the excess mulch and/or soil from the circumference of the trunk to the point where the trunk flares out into root growth. Make sure mulch is no thicker than several inches and away from the base of the trunk. 

Follow watering guidelines which is important for health and establishment of the tree. It can take up to two years for the root system to establish.  Newly planted trees do not require fertilizer. Here is our page on planting trees and shrubs including a video. https://extension.umd.edu/resource/planting-tree-or-shrub

Japanese beetles - Remove the beetle traps. Frequently, a single trap attracts beetles from the entire neighborhood and concentrates the damage in a small area close to the trap site.

The beetles favor this tree. If possible, handpick beetles and drop them into soapy water. Or hold the container with soapy water underneath a branch or stem where Japanese beetles are feeding. Gently tap the branch and the beetles will drop into the water.https://extension.umd.edu/resource/japanese-beetles-trees-shrubs-and-flowers

Monitor to see if the tree recovers.

Marian