| 
Data Structures and Algorithms 
with Object-Oriented Design Patterns in C# | 
Figure 
 shows an alternate representation of
the tree  
 defined in Equation 
.
In this case,
the tree is represented as a set of nested regions in the plane.
In fact, what we have is a Venn diagram 
which corresponds to the view that a tree is a set of sets.
   
Figure: An alternate graphical representation for trees.
This hierarchical, set-within-a-set view of trees is also evoked by considering the nested structure of computer programs. For example, consider the following fragment of C# code:
class D {
    class E {
	class F {
	}
    }
    class G {
	class H {
	    class I {}
	}
	class J {
	    class K {}
	    class L {}
	}
	class M {}
    }
}
The nesting structure of this program
and the tree given in Equation