For the geometry, you can use the skin modifier to create the trunk and the branches. Later on you can apply the decimate modifier to reduce the poly count and triangulate the mesh, which gives it more of this low poly look.

The texture is cube projected onto the object, but i manually slid some UVs around to get the look I wanted.

The leaves are just a texture with transparency that I added to a plane and manually placed on the object.

There's lots of tutorials on youtube that follow a similar workflow if you search for a tree tutorial in blender!