node id          parent node id

-------          --------------

100                 null           //this is the root node

101                 100

123                 101

124                 101

126                 101

103                 100

104                 100

109                 100

128                 109

122                 100

127                 122

129                 127

130                 129
	
AddChildNodes(TreeNode parentNode)
{
   var childNodeIds GetChildNodeIds(parentNode.Id);
   foreach (int childNodeId in childNodeIds)
   {
      TreeNode childNode = new TreeNode();
      //set other properties...

      //add to parent          
      parentNode.Nodes.Add(childNode);

      //call same function recursively
      AddChildNodes(childNode);
   }