What is the ruling on taking a tree branch from a non-Islamic garden that is entered for a fee, and what should be done after planting it, and what is the expiation?

The fundamental principle regarding trespass against public or private property is prohibition, unless with the permission of its owner or custodian. An exception is made for a trifling matter that people customarily overlook, as customary permission is akin to verbal permission. However, if an item has value and people do not tolerate its taking, or if taking it results in harm, then it is not permissible to take it.

Therefore, you must seek absolution from those responsible for the garden and offer to return the value of the seedling to them, or give them the value without their knowledge if you fear a greater harm [from informing them], such as purchasing something the garden needs or depositing the money into its account.