Best design pattern for multiple if statements in an interface impementation

I have an IComposer interface in my c# project:

public interface IComposer
{
    string GenerateSnippet(CodeTree tree);
}

CodeTree is a base class that contains a List<CodeTree> of classes that inherit from CodeTree. For example:

public class VariablesDecleration : CodeTree
{
     //Impl
}

public class LoopsDecleration : CodeTree
{
     //Impl
}

I can have a few classes that implement IComposer and in each I have the GenerateSnippet that loops over the List<CodeTree> and basically do:

foreach (CodeTree code in tree.Codes)
{
    if (code.GetType() == typeof(VariablesDecleration))
    {
        VariablesDecleration codeVariablesDecleration = (VariablesDecleration) code;
        // do class related stuff that has to do with VariablesDecleration
    }
    else if (code.GetType() == typeof(LoopsDecleration))
    {
        LoopsDecleration codeLoopsDecleration = (LoopsDecleration) code;
        // do class related stuff that has to do with LoopsDecleration
    }
}

I have this foreach and if statements repeating in each class that implements IComposer.

I was wondering if there is a better design pattern to handle such a case. lets say tommrow I add a new class that inherits from CodeTree - I would have to go over all the classes that implement IComposer and modify them.

I was thinking about the Visitor Design Pattern - but wasn't sure and not exactly sure if and how to implement it. Does Visitor even the right solution for this case?