This model is from DynaSCAPE Software's Sketch3D download site, a huge online database of landscape components for SketchUp. This model is one of the FREE models offered on the site for anyone to use. This model is made up of a 3D trunk and branches with 2D textures for the leaves to keep the poly count low for a tree of this size (just over 1500).
Note: When using models with 2D textures like this you will get the best appearance when you set your transparency quality to 'Medium' and uncheck the 'Use Anti-aliased Textures' option under Rendering in your model info.
Check out the huge collection of plants, garden structures, pools, ponds etc. at DynaSCAPE.com. You will also find textures and plugins created specifically for landscape modeling using SketchUp.