what kind of weed killer can I use on the weed trees
I have tried everything I can think of and struggle every year with these trees growing everywhere.
Your problem has two aspects: the tree seedlings, and the tree(s) that drops the seedlings. Can you eliminate the parent tree(s). If you can, this article talks about methods for killing trees: https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-kill-a-tree-killing-trees-in-your-garden.htm
If you can't get rid of the parent, you are left with no choice but to contend every year with the seedlings. This article will help: https://www.gardeningknowhow.com/ornamental/trees/tgen/weed-trees.htm