The tree count on the home dashboard includes trees which have been planted as part of your subscription (we plant trees every month per employee as well) and the tree count on the admin section shows just the trees planted when:
a user completes their first action
for every 10 actions a user completes
When looking at the data, the tree count will remain static regardless of the date range you select, as it always displays the "all time" total. The rest of the data will update based on the selected date range.