实现数据 Package 类以提取事件对象可能是最简单的方法：

final class WrapperDto {

    @Nullable
    @SerializedName("data")
    @Expose(serialize = false, deserialize = true)
    private final DataDto data;

    @SuppressWarnings("unused")
    private WrapperDto(@Nullable final DataDto data) {
        this.data = data;
    }

    @Nullable
    <E extends Event> E toEvent() {
        if ( data == null ) {
            return null;
        }
        return data.toEvent();
    }

    private static final class DataDto {

        @Nullable
        @SerializedName("tradeEvent")
        @Expose(serialize = false, deserialize = true)
        private final Event.Trade tradeEvent;

        @Nullable
        @SerializedName("errorEvent")
        @Expose(serialize = false, deserialize = true)
        private final Event.Error errorEvent;

        @SuppressWarnings("unused")
        private DataDto(@Nullable final Event.Trade tradeEvent, @Nullable final Event.Error errorEvent) {
            this.tradeEvent = tradeEvent;
            this.errorEvent = errorEvent;
        }

        @Nullable
        private <E extends Event> E toEvent()
                throws IllegalStateException {
            @Nullable
            Event bestEvent = null;
            for ( final Event event : new Event[]{ tradeEvent, errorEvent } ) {
                if ( bestEvent == null ) {
                    bestEvent = event;
                } else if ( event != null ) {
                    throw new IllegalStateException("Ambiguity detected. event=" + event.getClass().getSimpleName() + ", bestEvent=" + bestEvent.getClass().getSimpleName());
                }
            }
            @SuppressWarnings("unchecked")
            final E castBestEvent = (E) bestEvent;
            return castBestEvent;
        }

    }

}

我相信，这种方法比根据您的需要调整runtimetypeadapterfactory更容易实现。但是，实现自定义类型适配器可能会在读取时检测到不明确的字段，因此不会反序列化每个字段（这会花费更多的堆）。
上述方法将通过以下测试：

private static final Gson gson = new GsonBuilder()
        .disableHtmlEscaping()
        .excludeFieldsWithoutExposeAnnotation()
        .create();
...
try ( final JsonReader jsonReader = open("tradeEvent.json") ) {
    Assertions.assertTrue(gson.<WrapperDto>fromJson(jsonReader, WrapperDto.class).toEvent() instanceof Event.Trade);
}
try ( final JsonReader jsonReader = open("errorEvent.json") ) {
    Assertions.assertTrue(gson.<WrapperDto>fromJson(jsonReader, WrapperDto.class).toEvent() instanceof Event.Error);
}
Assertions.assertThrows(IllegalStateException.class, () -> {
    try ( final JsonReader jsonReader = open("tradeAndErrorEvent.json") ) {
        gson.<WrapperDto>fromJson(jsonReader, WrapperDto.class).toEvent();
    }
});