What's autumnalis? Sounds like only part of the name.

Whatever tree it is, there is a possibility that it has gone dormant to save itself. Time will tell.

Hi, welcome to GoY, off the top of my head I can think of at least 6 different plants, with the word 'autumnalis' in the name, but as you've called it a tree, I've asumed you mean Prunus x Subhirtella 'autumnalis Rosea, common name rosebud cherry, and should ideally been planted in the ground as soon as you received it, the pot is more than likely too small for the tree, and is now potbound, and unable to take up water and nutrients, knock it out of the pot, and if the roots are going round and round in circles, try to untangle them and preferably plant in the ground, using a hole twice as wide and deep as the rootball, mix some well rotted manure, garden compost, or other humus material into the soil you removed, put back into the planting hole until you reach the required depth for planting, {the top of the rootball level, or just below the level of the soil when firmed}, give it plenty of water for the rest of the summer at least, and it might just revive itself, Derek.