I'm trying to understand a binaray tree class. In the file is this class:

// Define tree nodes
public class TTreeNode 
{
   public string name;
   public double value; 
   public TTreeNode left, right;        // <-- What is this??
       
    // Constructor to create a single node 
	public TTreeNode (string name, double d) 
    {
          this.name = name;
          value = d;
          left = null;
          right = null;
    }
}

See comment in line. I don't understand that syntax.