Question 1.I want to change DirTree.CS to UserControl to place it in the Grid position specified in the figure.
How to achieve it?

Question 3:The right-click menu of any item in TreeView1 contains the possibility to add a SubItem or add an Item of the same level.
How to achieve it?

Question 6:When Double-Clicking any of Item in TreeView1 will display the TreeView2 in the same Grid position and the TreeView2 will diasplay all SubItems of the selected Item of the TreeView1.
How to achieve it?

    Question 8:The HeaderTemplate of The TreeView2 contains 6 <Image>. The first red arrow on the left is to return to display the TreeView1. The function of the second black arrow on the left is to display all SubItems of the previous Item of the current Item of the TreeView1 in the TreeView2. The function of the third black arrow on the left is to display all SubItems of the next Item of the current Item of the TreeView1 in the TreeView2. The three arrows behind are the same as those of the TreeView1
Filter all items in a specific way, and then display the filtered items out.
    How to achieve it?

That's great enthusiasm from you to use our diagram for everything in your life, but there's no point creating a treeview user control through diagram when WPF already comes with a perfectly fine dedicated control. E.g. see tuturial at https://www.c-sharpcorner.com/UploadFile/mahesh/treeview-in-wpf/ for styling TreeView etc.

You could place several TreeViews in a TabControl, or switch a single TreeView's data from ToolBar button clicks to implement your header UI.

    Thank you very much.

    I understand the example in this https://www.c-sharpcorner.com/UploadFile/mahesh/treeview-in-wpf/ link. But https://stackoverflow.com/questions/13420994/how-to-display-context-menu-for-tre
..., https://stackoverflow.com/questions/30953599/how-to-insert-a- child-item-in-a-tre...
There are some parts in these two examples that I don't understand very well, such as the meaning of context menu, but it doesn't matter, I will continue to understand.

    I would like to ask how the custom ComboBox style in the screenshot 11_17_14.png is realized? and add the corresponding item or sub-item of TreeView1 by clicking the item in the custom ComboBox. I tried to nest a TreeView or DataGrid in the ComboBox. But I feel that the effects are different.

    Any assistance from you is greatly appreciated.
   
    Send you the most sincere blessings.

    Jack.

    Thank you very much.
   
    I have tried the examples in the link, and there are some errors in them, but I don't know how to troubleshoot. I kindly ask you to write an example for me in combination with all the questions I raised above. Although I know this is just WPF knowledge, I really want to implement it quickly and work with MindFusion WPF Pack.

    Best wishes for you.

    Jack.