How to get lowest level of nesting list in c#

Question

l have class that have parent and child with same class, and I don't know how many levels there are, i want to get id of last child

class Model 
    {
         public Model Parent {get;set;}
         public List<Model> Child {get;set;}
         public string modelId {get;set;}
         public bool HasChild {get;set;}
    }

I have tried this way

var modelIds = Models.Where(e=>!e.HasChild).Select(e=>e.ModelId).ToList()

i cant find a way to get the last modelId