childrenS :定义parentS <-> protobuf关系

Question

如何在proto中定义parentS <-> childrenS关系

syntax = "proto3";

message Root {
     repeated Category category = 2;  
}

message Category {
     string name = 2;
     repeated Category parent = 3; 
}

这里的关键是我希望能够召唤孩子们

MamyCategoryInstance
|
|--- FooCategoryInstance
...//

PapaCategoryInstance
|
|---- FooCategoryInstance
|---- BarCategoryInstance

谢谢