Example for saving & loading node states with DevExpress TreeList.

frmMyTest.cs

using System;
namespace Example
{
    public partial class dxMyForm : DevExpress.XtraBars.Ribbon.RibbonForm
    {
        
        private TreeListViewState treeListViewState;
        public dxMyForm()
        {
            InitializeComponent();

        }
    
        private void dxMyForm_Load(object sender, EventArgs e)
        {
            treeListViewState = new TreeListViewState(treeList1);
            LoadData();
        }

        private void LoadData()
        {
            treeList1.DataSource = DataTable..
        }

        private void treeList1_FocusedNodeChanged(object sender, DevExpress.XtraTreeList.FocusedNodeChangedEventArgs e)
        {
            treeListViewState.SaveState();
        }

        private void treeList1_NodesReloaded(object sender, EventArgs e)
        {
            treeListViewState.LoadState();
        }
    }
}

TreeListViewState.cs

using System.Collections;
using DevExpress.XtraTreeList;
using DevExpress.XtraTreeList.Nodes;
using DevExpress.XtraTreeList.Nodes.Operations;

public class TreeListViewState
{
    private ArrayList expanded;
    private ArrayList selected;
    private object focused;
    private object topNode;

    public TreeListViewState() : this(null) { }
    public TreeListViewState(TreeList treeList)
    {
        this.treeList = treeList;
        expanded = new ArrayList();
        selected = new ArrayList();
    }

    public void Clear()
    {
        expanded.Clear();
        selected.Clear();
        focused = null;
        topNode = null;
    }
    private ArrayList GetExpanded()
    {
        OperationSaveExpanded op = new OperationSaveExpanded();
        TreeList.NodesIterator.DoOperation(op);
        return op.Nodes;
    }
    private ArrayList GetSelected()
    {
        ArrayList al = new ArrayList();
        foreach (TreeListNode node in TreeList.Selection)
            al.Add(node.GetValue(TreeList.KeyFieldName));
        return al;
    }

    public void LoadState()
    {
        TreeList.BeginUpdate();
        try
        {
            TreeList.CollapseAll();
            TreeListNode node;
            foreach (object key in expanded)
            {
                node = TreeList.FindNodeByKeyID(key);
                if (node != null)
                    node.Expanded = true;
            }
            TreeList.FocusedNode = TreeList.FindNodeByKeyID(focused);
            foreach (object key in selected)
            {
                node = TreeList.FindNodeByKeyID(key);
                if (node != null)
                    TreeList.Selection.Add(node);
            }

        }
        finally
        {
            TreeList.EndUpdate();
            TreeListNode topVisibleNode = TreeList.FindNodeByKeyID(topNode);
            if (topVisibleNode == null) topVisibleNode = TreeList.FocusedNode;
            TreeList.TopVisibleNodeIndex = TreeList.GetVisibleIndexByNode(topVisibleNode);
        }
    }
    public void SaveState()
    {
        if (TreeList.FocusedNode != null)
        {
            expanded = GetExpanded();
            selected = GetSelected();
            focused = TreeList.FocusedNode[TreeList.KeyFieldName];
            topNode = TreeList.GetNodeByVisibleIndex(TreeList.TopVisibleNodeIndex)[TreeList.KeyFieldName];
        }
        else
            Clear();
    }

    private TreeList treeList;
    public TreeList TreeList
    {
        get
        {
            return treeList;
        }
        set
        {
            treeList = value;
            Clear();
        }
    }

    class OperationSaveExpanded : TreeListOperation
    {
        private ArrayList al = new ArrayList();
        public override void Execute(TreeListNode node)
        {
            if (node.HasChildren && node.Expanded)
                al.Add(node.GetValue(node.TreeList.KeyFieldName));
        }
        public ArrayList Nodes { get { return al; } }
    }
}

Add [TreeListViewState.cs] to your project than use it as in example..
Tricky part is you need to load the nodes treeList1_NodesReloaded event.