Werk #12963: Fix BI aggregation work tree

Component	User interface
Title	Fix BI aggregation work tree
Date	Jun 17, 2021
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.1.0b1 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME) 2.0.0p6 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME) 1.6.0p25 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME)

Sometimes several trees were opened when a single tree was clicked to open.

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