Update: 23th Sept 2021
Version 1.23 of FranceVFR Airport France Pack and Clermont-Ferrand single airport product
fixed the tree issue and my temporary Tree fix is not usefull anymore. Download the FranceVFR update via your FranceVFR personnal account (https://www.vfrnetwork.com/shop/fr/mon-compte) and re-download your product.
This very simple fix removes unwanted trees on runway 26 at LFLC - Clermont-Ferrand airport scenery from FranceVFR after World Update 6.
IMPORTANT: This is just temporary fix. When MSFS get fixe or FranceVFR release an official patch don't forget to remove this.