public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
{
    if (sourceType == typeof(string))
    {
        return true;
    }

    return base.CanConvertFrom(context, sourceType);
}

public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
{
    if (value is string)
    {
        // parse the string, return a new node
    }

    return base.ConvertFrom(context, culture, value);
}

var str = "{"Username":"123","Name":"Test Name","Degree":0}";
var deserialized = JsonConvert.DeserializeObject<Node>(str);