Tree Planting Fail

Tree Planting Fail

I live in the Piedmont of NC. I got three Yaupon Holly trees from an online mail order source in the first part of October. After they arrived I couldn't get them in the ground for about 4 days. I thought I did the right things planting them, dug a hole significantly bigger than the modest root ball (these guys are only about a foot tall) and used new bagged topsoil to fill it up. Watered every three days unless it rained (which it has been, quite a bit, but they are on the top of a slope so I expect drainage isn't much of an issue) for the first 2 weeks they were in the ground. Now their leaves have turned a nice red brown and have fallen off and I expect they are dead. Any suggestions as to what went wrong?
The Name that Plant Game!:)

The Name that Plant Game!:)

Seeking some advice

Seeking some advice

New here

New here

help! I am killing a tree

help! I am killing a tree

so my room is clean for once.

so my room is clean for once.

Angel wing Begonia

Angel wing Begonia