Asigning Default Values To List Of Binary Tree Elements - Missing Constructor?

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C#

constructor

exceptions

Alright, I'm having hard time figuring our how I can assign default values to the elements of the list (Trees and nodes) so I don't get NullReferenceException.

The basic idea of the code is:
List contains from Trees, each tree contains 2 nodes, each node contains 2 sub-nodes.
______________________________
|...L.N...................R.N..........|
|.../..\...................../ \..........| <---Each List[i] contains the following.
|L.N...R.N........L.N...R.N......|
------------------------------

Each node contains Name(string) and Size(Int) Data.
code:

class Program
{
    static void Main(string[] args)
    {
        List<Tree> TreeList = new List<Tree>();

        Tree newtree = new Tree();
        Branch newbrach = new Branch();

        // user can add any number of new trees to the list
        // when tree is added, user can edit the default values of the tree

        foreach (Tree item in TreeList)
        {
            //loop to print out all values
        }

    }

 }

class Tree
    {
        public Branch Left = new Branch();
        public Branch Right = new Branch();
    }

class Area
{
    public string Name;
    public int Size;
}

class Branch
{
    public Area Area = new Area();
    public Branch Right;
    public Branch Left;
}

I must be missing a constructor of some sort, because if I'm adding new tree the the list and I'm trying to directly edit it via List[i].Left.Area.Name = ... I get NullReferenceExeption.

Basically, what I want is - whenever I add a new Tree to the list, each node should have it's default values set to 0 or something that can be manually changed later.