Gettting rest data to late due to async

Hello,

i have TabbedPage, which every tab needs to be filled with different data. My REST request works but the data ist not available at the time i need it.

in My RootPage where everything starts i create a Master Detail Page which includes

var tabbedPage = new TabbedPage {
                Title = "Open Tasks",
                Children = {
                    openTasks,
                    completedTasks,
                    missedTasks
                },
                CurrentPage = openTasks,
            };

also their i execute my call on the start

protected override void OnAppearing (){

            ViewModel.TaskCommand.Execute (null);
        }

In my MainViewModel i have following

public Command TaskCommand {
            get { return taskCommand ?? (taskCommand = new Command (async () => await ExecuteTaskCommand ())); }
        }

        public async Task ExecuteTaskCommand ()
        {
            if (IsBusy) {
                return;
            }

            IsBusy = true;

            try{
                var taskResponse = await teamService.GetTasks();

                foreach (var task in taskResponse) {
                    Tasks.Add(task);

                }

                OnPropertyChanged("Tasks");

            } catch (Exception ex) {
                Debug.WriteLine (ex);
            }

            IsBusy = false;
        }

When i Debug.WriteLine in my MainViewModel it gets the Data. But when i try to acces the data in my RootPage ViwModel.Tasks are empty.
I think thats a problem with the asynchronous but i don't really know how to handle this.