feat: update insert sibling logic

Author: SSShooter

src/dev.ts

@@ -63,7 +63,8 @@ const mind = new MindElixir(options)
 
 const data = MindElixir.new('new topic')
 console.log(data)
-mind.init(example)
+// mind.init(example)
+mind.init(data)
 function sleep() {
   return new Promise<void>(res => {
     setTimeout(() => res(), 1000)

src/nodeOperation.ts

@@ -90,6 +90,10 @@ export const insertSibling = function (this: MindElixirInstance, el?: Topic, nod
   if (nodeObj.root === true) {
     this.addChild()
     return
+  } else if (nodeObj.parent?.root === true && nodeObj.parent?.children?.length === 1) {
+    // add at least one node to another side
+    this.addChild(findEle(nodeObj.parent!.id))
+    return
   }
   const newNodeObj = node || this.generateNewObj()
   insertNodeObj(nodeObj, newNodeObj)