IQueryable expression type mismatch

I want to create an extension method for a LINQ expression but I'm stuck. What I need is just to create a method which will add a specific Where clause to a Queryable. Something like:

var hierarchy = "a string";
Session.Query<SomeClass>.Where(x => x.Layer.Hierarchy.StartsWith(hierarchy) ||
                                    x.Layer.Hierarchy == hierarchy);

to become:

var hierarchy = "a string";
Session.Query<SomeClass>.LayerHierarchy(x => x.Layer, hierarchy);

And do that Where logic inside. So basicly the extension method LayerHierarchy() is running over the Queryable of T but the subject is of type Layer:

public static IQueryable<T> LayerHierarchy<T>(this IQueryable<T> query,
                                                  Expression<Func<T, Layer>> layer,
                                                  string hierarchy)

{
    var parameterExp = Expression.Parameter(typeof(Layer), "layer");
    var propertyExp = Expression.Property(parameterExp, "Hierarchy");

    // StartWith method
    MethodInfo methodStartsWith = typeof(string).GetMethod("StartsWith", new[] { typeof(string) });
    var valueStartsWith = Expression.Constant(string.Concat(hierarchy, "|"), typeof(string));

    var methodExpStartsWith = Expression.Call(propertyExp, methodStartsWith, valueStartsWith);
    var startsWith = Expression.Lambda<Func<Layer, bool>>(methodExpStartsWith, parameterExp);

    // Equals method
    MethodInfo methodEquals = typeof(string).GetMethod("Equals", new[] { typeof(string) });
    var valueEquals = Expression.Constant(hierarchy, typeof(string));

    var methodExpEquals = Expression.Call(propertyExp, methodEquals, valueEquals);
    var equals = Expression.Lambda<Func<Layer, bool>>(methodExpEquals, parameterExp);

    return query
                .Where(startsWith)
                .Where(equals);
}

Everything works fine above the return line. It complains that...

Cannot convert from System.Linq.Expressions.Expression<System.Func<Layer, bool>> to System.Linq.Expressions.Expression<System.Func<T, int, bool>>

when trying to pass the expressions to query.Where() method. How can I fix it?