The photo you sent looks like a sapling or young woody plant of either a butterfly bush (buddleah) or a native tree from your area. Are the back of the leave slightly fuzzy? Are there panicles of  buds that hang in clusters and bloom purple or pink? That would indicate a buddleah.  Sometimes not just native plants pop up in landscapes but shrubs purchased at a nursery can cast seeds about and volunteer as new plants. In most cases they should be removed as they can grow too large for the space where they volunteer and crowd out other plants but if you like the newcomer, you can let it grow and see what happens. It is your garden and there are no rules. Keep growing, Marianne Binetti