Is it possible that there is a memory leak when InsertMany is used?

I created a simple program GIST and get the following output in pprof

Showing nodes accounting for 22425.05kB, 100% of 22425.05kB total
Showing top 10 nodes out of 23
flat flat% sum% cum cum%
16144.01kB 71.99% 71.99% 22425.05kB 100% main.main.func2
3638.89kB 16.23% 88.22% 3638.89kB 16.23% github.com/mongodb/mongo-go-driver/core/wiremessage.Query.AppendWireMessage
1536.07kB 6.85% 95.07% 1536.07kB 6.85% github.com/mongodb/mongo-go-driver/bson.newElement
553.04kB 2.47% 97.53% 553.04kB 2.47% github.com/mongodb/mongo-go-driver/bson.NewDocument
553.04kB 2.47% 100% 6281.04kB 28.01% github.com/mongodb/mongo-go-driver/mongo.(*Collection).InsertMany
0 0% 100% 553.04kB 2.47% github.com/mongodb/mongo-go-driver/bson.ElementConstructor.ArrayFromElements
0 0% 100% 512.02kB 2.28% github.com/mongodb/mongo-go-driver/bson.ElementConstructor.ObjectID
0 0% 100% 1024.05kB 4.57% github.com/mongodb/mongo-go-driver/bson.ElementConstructor.SubDocument
0 0% 100% 553.04kB 2.47% github.com/mongodb/mongo-go-driver/bson.NewArray
0 0% 100% 1024.05kB 4.57% github.com/mongodb/mongo-go-driver/bson.ValueConstructor.Document

When I use the same simple program and add every struct one by one with InsertOne, I cannot see that something is waiting to get garbage collected.