HI,

You can change the default view mode using project_view.xml file of project module:

<field name="view_id" ref=" view_project "></field>  <!-- For Tree View -->

instead of

<field name="view_id" ref="view_project_kanban"/>

OR:

Edit the action(Settings/Technical/Actions/Window Actions) with name: Projects and give tree view reference of project.project.tree in View Ref.