Create Expression Trees with a lambda C# with Example

expression 
Following is most basic expression tree that is created by lambda. 
Expression> lambda = num => num == 42; 
To create expression trees 'by hand', one should use Expression class. 
Expression above would be equivalent to: 
ParameterExpression parameter = Expression.Parameter(typeof(int), "num"); // num argument 
ConstantExpression constant = Expression.Constant(42, typeof(int)); // 42 constant 
BinaryExpression equality = Expression.Equals(parameter, constant); // equality of two expressions 
(num == 42) 
Expression> lambda = Expression.Lambda>(equality, parameter);