Most Common Custom WebParts Part 1 – Tree View WebPart Shows Sites and Sub-Sites

I desired to support most common custom webparts used by the SharePoint professional, so that these can be helpful for them.
A custom tree view webpart shows all the sites and sub-sites of a SharePoint site

SharePoint Custom Tree View WebPart

Please use the below code and to get the exact look as show in the aboave image, the tree view webpart can expand/collapse

using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;

namespace CustomWebParts.CustomTreeView
{
    [ToolboxItemAttribute(false)]
    public class CustomTreeView : WebPart
    {
        // Visual Studio might automatically update this path when you change the Visual Web Part project item.
        //private const string _ascxPath = @"~/_CONTROLTEMPLATES/CustomWebParts/CustomTreeView/CustomTreeViewUserControl.ascx";

        TreeView myTree;
        LinkButton lnkBtnExpand;
        LinkButton lnkBtnCollapse;
        Label lblPipeDivider;
        Label lbl_ErrorMsg;
        private string errorMessage = string.Empty;
        private int level = 0;

        protected override void CreateChildControls()
        {
            //Control control = Page.LoadControl(_ascxPath);
            //Controls.Add(control);

            this.Controls.Clear();
            myTree = new TreeView();
            myTree.ExpandImageUrl = "/_layouts/images/tvplus.gif";
            myTree.RootNodeStyle.ImageUrl = "/_layouts/images/stsicon.gif";
            myTree.ParentNodeStyle.ImageUrl = "/_layouts/images/stsicon.gif";
            myTree.LeafNodeStyle.ImageUrl = "/_layouts/images/stsicon.gif";
            myTree.CollapseImageUrl = "/_layouts/images/tvminus.gif";            
            myTree.NoExpandImageUrl = "/_layouts/images/stsicon.gif";            

            myTree.NodeWrap = true;
            myTree.ShowLines = true;
            myTree.ShowExpandCollapse = true;
            myTree.EnableClientScript = true;

            GenerateTreeView();
            myTree.CollapseAll();
            myTree.CssClass = "ms-navitem a";
            this.Controls.Add(myTree);

            lnkBtnExpand = new LinkButton();
            lnkBtnExpand.Click += new EventHandler(expandAll_Click);
            lnkBtnExpand.Text = "Expand all";
            lnkBtnExpand.CssClass = "ms-navitem a";
            this.Controls.Add(lnkBtnExpand);

            lblPipeDivider = new Label();
            lblPipeDivider.Text = "  |  ";
            this.Controls.Add(lblPipeDivider);

            lnkBtnCollapse = new LinkButton();
            lnkBtnCollapse.Click += new EventHandler(collapseAll_Click);
            lnkBtnCollapse.Text = "Collapse all";
            lnkBtnCollapse.CssClass = "ms-navitem a";
            this.Controls.Add(lnkBtnCollapse);

            lbl_ErrorMsg = new Label();
            this.Controls.Add(lbl_ErrorMsg);

            base.CreateChildControls();
        }

        private void GenerateTreeView()
        {
            SPSite mySite = null;
            SPWeb myWeb = SPContext.Current.Web;
            SPSecurity.RunWithElevatedPrivileges(delegate()
            {
                try
                {
                    mySite = new SPSite(myWeb.Site.ID);
                    using (mySite)
                    {
                        level = 1;
                        foreach (SPWeb subWeb in myWeb.Webs)
                        {
                            TreeNode myTreeNode = new TreeNode(subWeb.Title);
                            myTreeNode.NavigateUrl = subWeb.Url;
                            ReadSubSites(subWeb, ref myTreeNode);
                            myTree.Nodes.Add(myTreeNode);
                        }

                    }
                }
                catch (Exception ex)
                {
                    errorMessage = ex.ToString();
                }
            });
        }

        private void ReadSubSites(SPWeb subWeb, ref TreeNode myTreeNode)
        {
            try
            {
                foreach (SPWeb myChildSubWeb in subWeb.Webs)
                {
                    TreeNode subnode = new TreeNode(myChildSubWeb.Title);
                    subnode.NavigateUrl = myChildSubWeb.Url;

                    myTreeNode.ChildNodes.Add(subnode);

                    if (myChildSubWeb.Webs.Count > 0)
                    {
                        if (myTreeNode.ChildNodes.Count > 0)
                        {
                            level = level + 1;
                            TreeNode myChildNode = myTreeNode.ChildNodes[myTreeNode.ChildNodes.Count - 1];
                            ReadSubSites(myChildSubWeb, ref myChildNode);                           
                            level = level - 1;
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                errorMessage = ex.ToString();
            }
        }

        void expandAll_Click(object sender, EventArgs e)
        {
            myTree.ExpandAll();
        }

        void collapseAll_Click(object sender, EventArgs e)
        {
            myTree.CollapseAll();
        }      

        protected override void RenderContents(HtmlTextWriter writer)
        {
            EnsureChildControls();
            lnkBtnExpand.RenderControl(writer);
            lblPipeDivider.RenderControl(writer);
            lnkBtnCollapse.RenderControl(writer);
            RenderChildren(writer);
        }      
    }
}