Okay i have found my mistake, i have to create the new Listuebung in the for-loop. Because of this mistake, the informations was added to the listfor every new head element
List<String> uebung;
//size is the filled list from Trainingsplansammlung
for(int i=0;i<list.size();i++){
uebung = new ArrayList<String>();
//set Head
dataHead.add(list.get(i).getName());
//set Childs
uebung.add(String.valueOf(list.get(i).getGewicht()));
uebung.add(String.valueOf(list.get(i).getWdhlg()));
uebung.add(String.valueOf(list.get(i).getSaetze()));
uebung.add(String.valueOf(list.get(i).getKommentar()));
uebung.add(String.valueOf(list.get(i).getEinheit()));
dataChild.put(dataHead.get(i), uebung);
}