Add ImageIndex to Treeview

It doesn't look like you would need the for loop. You can do the same much simpler with a foreach and a little bit of linq:

// assuming they are ints
var AnalogImagesIndex = 0;
var TrendImageIndex = 2;

// simplifies the ifs
var imageIndicies = new Func<string, int?>[]
{
    attr => attr == "server.point.AV" ? AnalogImagesIndex : (int?)null,
    attr => attr.StartsWith("trend") ? TrendImageIndex : (int?)null,
    // ...
};

var imageIndex = imageIndicies
    .Select(x => x(xNode.Attributes["NAME"].Value))
    .First(x => x.HasValue)
    .Value;

To do the rest you can use the helper from BCdotWEB's answer.

Another assumption is that there is no else at the end, otherwise you need to use FirstOrDefault or provide an else lambda.

or with even less repetition the extreme solution:

var getImageIndexOrDefault = new Func<bool, int, int?>(
    (condition, value) => condition ? value : (int?)null);

var imageIndicies = new Func<string, int?>[]
{
    attr => getImageIndexOrDefault(attr == "server.point.AV", AnalogImagesIndex),
    attr => getImageIndexOrDefault(attr.StartsWith("trend"), TrendImageIndex),
};

The moment you start copy-pasting code and only changing one small thing, it's time to move that code to a method.

private void CreateAndAddNode(WhateverTypeImagesIndexIs imagesIndex, int x)
{
    var tNode2 = new TreeNode(xNode.Attributes["NAME"].Value, imagesIndex, imagesIndex);
    inTreeNode.Nodes.Add(tNode2);
    tNode2 = inTreeNode.Nodes[x];
    AddNode(xNode, tNode2);
}

I'm assuming AnalogImagesIndex etc. all inherit from some base type; that's the one to use as the method's parameter.

Moreover, all of those ifs can be changed to a switch.

On top of @BCdotWEB & @t3chb0t answers you can use the .Any() condition.

For example:

List<string> group1 = new List<string> {"schedule.NSPDigitalSchedule, schedule.Whatever, WhenEver.WhatEver"};

List<string> group2 = ...

 //in foreach loop:
string nodeValue = xNode.Attributes["TYPE"].Value;
if (group1.Any(m=>m==nodeValue)) 
{
   //Call the method for adding image for group1
   continue; //This will go to the next iteration so you don't need nested if's
}

if (group2.Any(m=>nodeValue.StartWith(m)) 
{
    //Call the method for adding image for group2
   continue; 
}

//and so on.