How to store Data in Cache object in C# ?

Hii i developed a web part in c#. and i used splist to fill data in treeview control. now i need to store this all data in Cache object so i can use this for post back page.

So how do i store data in Cache object ??

public void FilParentTreeNode()
         {
             try
             {
                 SPList projectlist = web.Lists["Projects List"];
                 SPList phase = web.Lists["Project Phases"];
                 SPList milestone = web.Lists["Project Milestones"];
                 SPList issue = web.Lists["Project Issues"];
 
 
 
                 SPQuery query = new SPQuery();
 
                 if (StrFilterProject == "")
                 {
 
                     query.ViewFields = "<FieldRef Name=\"Title\"/><FieldRef Name='Log_x002e__x0020_FinalDispState' /><FieldRef Name='Start_x0020_Date' /><FieldRef Name='End_x0020_Date' /><FieldRef Name='Status' />";
 
                     query.Query = "<Query><OrderBy><FieldRef Name='OS' /><FieldRef Name='Title' /><FieldRef Name='Log_x002e__x0020_FinalDispState' /><FieldRef Name='Start_x0020_Date' /><FieldRef Name='End_x0020_Date' /><FieldRef Name='Status' /></OrderBy></Query>";
                 }
                 else
                 {
                     query.ViewFields = "<FieldRef Name=\"Title\"/><FieldRef Name='Log_x002e__x0020_FinalDispState' /><FieldRef Name='Start_x0020_Date' /><FieldRef Name='End_x0020_Date' /><FieldRef Name='Status' />";
 
                     query.Query = "<OrderBy><FieldRef Name='OS' /><FieldRef Name='Title' /><FieldRef Name='Log_x002e__x0020_FinalDispState' /><FieldRef Name='Start_x0020_Date' /><FieldRef Name='End_x0020_Date' /><FieldRef Name='Status' /></OrderBy><Where><Eq><FieldRef Name='Title' /><Value Type='Text'>" + StrFilterProject + "</Value></Eq></Where>";
                 }
 
                 SPListItemCollection item = projectlist.GetItems(query);
                 
                 if (StrFilterProject == "")
                 {
                     ddlist.DataSource = item;
                     ddlist.DataBind();
                 }
 
                 foreach (SPListItem itemdata in item)
                 {
 
                     TreeNode project = new TreeNode();
                     
                     project.ToolTip = "Project List";
                    
 
                     try
                     {
                         if (itemdata["Start_x0020_Date"] == null)
                         {
                             itemdata["Start_x0020_Date"] = "1900-01-01 00:00:00.000";
                            
                         }
 
                         if (itemdata["End_x0020_Date"] == null)
                         {
                             itemdata["End_x0020_Date"] = "1900-01-01 00:00:00.000";
                         }
                         if (itemdata["Status"].ToString() == "Open")
                         {
                             project.Text = "<b> <Font Color=Green>" + itemdata["Title"].ToString() + "</font></b>" + "<font color=Red>" + "--" + "</font>"  + DateTime.Parse(itemdata["Start_x0020_Date"].ToString()).ToShortDateString() + "<font color=Red>" + "--" + "</font>" + DateTime.Parse(itemdata["End_x0020_Date"].ToString()).ToShortDateString() + "<font color=Red>" + "--" + "</font>" + itemdata["Log_x002e__x0020_FinalDispState"].ToString();
                         }
                         else
                         {
                             project.Text = "<b> <Font Color=Black>" + itemdata["Title"].ToString() + "</font></b>" + "<font color=Red>" + "--" + "</font>"  + DateTime.Parse(itemdata["Start_x0020_Date"].ToString()).ToShortDateString() + "<font color=Red>" + "--" + "</font>" + DateTime.Parse(itemdata["End_x0020_Date"].ToString()).ToShortDateString() + "<font color=Red>" + "--" + "</font>" + itemdata["Log_x002e__x0020_FinalDispState"].ToString();
                         }
//                         project.Text = itemdata["Title"].ToString() ;
                         project.Value = itemdata["Title"].ToString();
                         
                         tv.Nodes.Add(project);
                         project.SelectAction = TreeNodeSelectAction.SelectExpand;
                         project.PopulateOnDemand = true;
                         //       parent.SelectAction = TreeNodeSelectAction.Expand;
 
                         
                       
                        //     project.Collapse();
                       
                   //      project.PopulateOnDemand = false;
                        
                     }
                     catch { }
 
                     
                 }
           //      if (ViewState["Value"] != null)
           //      {
           ////          ((TreeNode)ViewState["Node"]).Parent.Expand();
                     
           //      }
                
             }
             catch { }
             
                  
               }

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