You have to assign a span width to tell the nested group how many columns of the parent group it needs to cross. In the appearance column for a nested group/repeat when you assign it a value of say w3 you're telling it to be 3 columns wide, you're not telling it how many columns of the parent group to span. It will force those 3 columns into 1 column of the parent group.
To set the span you add a colon and number of columns in the parent group you want it to span. Continuing with our example, lets say the parent group has 4 columns (w4). If you want the nested group with 3 columns to span all 4 of the parent group columns you would format the appearance of the nested group as w3:4. If you wanted it to span 2 columns of the parent group you would put in w3:2
Your Seedling Count group is w3 and your Sapling group is also w3. So to span the entire Seedling Count group, you would set your Sapling group's appearance to w3:3.