This tree may not be dead, but it's leaves are for sure. It could be in early dorminancy, chemical damage, or related to all those flowers competing for resources in the planting box. I recommend waiting until next spring to see if it leafs out. This tree most likely won't fall even if dead because it has a bunch of leaves, so it was obviously healthy enough to bloom in the spring, so its not exactly a rotting dead.

They finally removed the tree and installed a new one which looks like it has died from the recent heat wave.

tree has been replaced