Child form not showing up in MDIcontainer's split Container

[marinajogy]

Do not use the Splitcontainer here

Use the Splitter instead.

On your MDI Parent, remove the Splitcontainer.
Add the Splitter control ( from All Windows Controls in the Toolbox ), add your Treeview inside that Splitter.
This will ensure that your Treeview, always occupies the left side of your form, and your child forms will always show on the right.

I hope you come right

thanksm, solved