Your tree does look like level 3. However, I've read that you'll need the tree to reach level 4 (50 hours and 50 days/able to sit by town tree) to sell your town to Tom Nook.
Level 1: 1 hour and 1 day played (Single cluster of leaves)
Level 2: 5 hours and 5 days played (Two clusters of leaves)
Level 3: 20 hours and 20 days played (Three clusters of leaves)
Level 4: 50 hours and 50 days played (Five clusters of leaves) (Player able to sit on planter box)
Level 5: 100 hours and 100 days played (Ten clusters of leaves, with a vine on the trunk)
Level 6: 180 hours and 180 days played
Level 7: 300 hours and 300 days played
Level 8: 500 hours and 500 days played (Seventeen+ clusters of leaves. Vines also encircle the trunk. Trunk covers the entire planting box)
https://animalcrossing.fandom.com/wiki/Plaza
https://www.belltreeforums.com/show...-Don-t-try-to-see-how-much-your-town-is-worth
https://www.belltreeforums.com/showthread.php?420879-Guide-for-selling-your-town-Updated-19-06-2017
https://www.belltreeforums.com/showthread.php?409947-Doesn-t-give-me-option-to-sell-my-town
https://www.reddit.com/r/AnimalCrossing/comments/5auape/all_your_questions_about_selling_your_town/
https://gamefaqs.gamespot.com/3ds/9...ew-leaf/answers/444896-how-can-i-sell-my-town