How the tree component in elementUI expands the first node by default when loading for the first time

elementUI
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is used in the project. How to implement the default deployment of the first level after the initial load?

Apr.02,2021

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look at the document

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3774b-2c08b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3774b-2c08b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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