<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
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**Do you want to request a *feature* or report a *bug*?**

bug.

**What is the current behavior?**

```js
  renderer.create(
    <Fragment>
      <Fragment>foo</Fragment>
    </Fragment>
  )
  .toTree()
```

> Invariant Violation: toTree() does not yet know how to handle nodes with tag=10

https://codesandbox.io/s/olky92m01y

**What is the expected behavior?**

returns a tree.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

16.2.0

const index = parentInstance.children.indexOf(child);
  if (index !== -1) {
    parentInstance.children.splice(index, 1);
  }
  parentInstance.children.push(child);
}
function insertBefore(
  parentInstance: Instance | Container,
  child: Instance | TextInstance,
  beforeChild: Instance | TextInstance,
): void {
  const index = parentInstance.children.indexOf(child);
  if (index !== -1) {
    parentInstance.children.splice(index, 1);
  }
  const beforeIndex = parentInstance.children.indexOf(beforeChild);
  parentInstance.children.splice(beforeIndex, 0, child);
}
function removeChild(
  parentInstance: Instance | Container,
  child: Instance | TextInstance,
): void {
  const index = parentInstance.children.indexOf(child);
  parentInstance.children.splice(index, 1);
}
const TestRenderer = ReactFiberReconciler({
  getRootHostContext() {
    return emptyObject;
  },
  getChildHostContext() {