To import into your scene go to File>Append, navigate to .blend files folder, open the file, open "Group" folder, then double-click on the name of the group and append.

The name of the model and the name of the group is the same.

             Betula_0205(4.8m)

             Betula_0204(5.1m)

             Betula_0203(5.5m)

             Betula_0202(5.8m)

             Betula_0201(6.5m)

Or you can select it and copy it using CTRL+C and in your scene pressing CTRL+V.

Please note that this scene contains textures from Poliigon.com and Vitaly  - Textures may not be redistributed

HDRI maps are from HDRI Haven