Model Tree panel is a Reference structure of Data.

Selection of an element can be made by choosing any layer from this model tree.  There is an eye symbol with each viewport which allows to Toggle on/off any element from the model. You can hide or unhide all the 2D or 3D structure from the entire model.

This structure can be break by Categories, Content, reality Data etc. by dropdown arrow symbol. Each properties shows all associated data attributes by selecting them. 

For Reality Data, it will show all the reality data properties and their attributes.

It is also coordinated with Bing Map. You can turn off/on the geo location by clicking on that Eye symbol.

  

If there any 2D structure created in the model, then it allows to see the entire model in 2D view by simply clicking on the 2D view option.

After selecting any element, 'Properties' icon shows the information about  Model Source, Source Information along with object properties.