You can access Tree View from Board View page, Jira Issue page Filters section and or as a Dashboard Item (Gadget).
To access Tree View from Jira Issue page user can follow the below steps:
Simply open a Jira Issue page, scroll down to Activity section and select Links Explorer from the available tabs or from the Comments drop down menu.
Or, Click on Jira Software Cloud home icon
Click on Projects and select a project
Select Issues section from the left side bar
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Choose an issue
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Select Links Explorer by clicking on the Links Explorer Tab in the Activity section
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To access Tree View from Board View page user can follow the below steps:
Open the project page by clicking on Projects menu and then select your desired project.
Click on Backlog/Active sprints present on the left side
Select the issue on which the user wants to access the tree view
Select Links Explore by clicking on Comments drop down under Activity section
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To access the Tree view as a Dashboard Gadget, please follow this documentation guide.