All I needed to do was set the layer blend mode to "Multiply" to get rid of the background but still keep the tree and shadow.

我所需要做的是把图层的混合模式改为“正片叠底”，通过这种方式来在保留树及其阴影的同时去掉背景。

youdao

In other photos, a wreath in the shape of a Christmas tree dangles above highway construction, and a "Happy Holidays" banner casts its shadow on a highway empty except for a single truck.

WSJ: rom Lee Friedlander at Janet Borden Gallery