At least 16,000 more trees have been planted here since 2007 and these grew out of an idea from Mrs Kirtida Mekani, one of this year's winners of the President's Award for the Environment.
She thought of a scheme that allowed people to plant a tree sapling in return for a donation and suggested this to the National Parks Board (NParks). Together she and NParks worked on this for two years before the Plant-A-Tree Programme came into fruition in 2007.
Today, participants can plant a tree sapling by donating $200.
Mrs Mekani, who helps out at her husband's trading company, said the idea took root when they first arrived here from India in 1990.
"The memory of our scenic drive from Changi Airport and its endless stretch of greenery was our first introduction to the country.
A LIVE WELL LIVED
I believe that we all have our part to play in this journey of life. Perhaps loving and promoting nature in my home of Singapore is my calling. Along the way, if my efforts, however small, have inspired others to actively pursue their passions, making our community a better place - then my life will have been well lived.
MRS KIRTIDA MEKANI, on her work in keeping Singapore green
"That perfect image has been permanently etched into my mind, a picturesque greeting card welcoming every visitor to this urban garden," said the 56-year-old, who is now a Singapore citizen and a member of the Garden City Fund Management Committee.
"As the memory of that day kept circling in my mind, so too did one particular question, 'I'm enjoying nature's bounty every day. Now, what can I do to give back?' "
Mrs Mekani, who had served as the founding executive director of the Singapore Environment Council, was recently awarded the President's Award for the Environment to recognise her outstanding environmental contributions.
Apart from the Plant-A-Tree Programme, Mrs Mekani is also an ambassador for the NParks' Community in Bloom programme, where people can come together and set up their own community gardens.
Mrs Mekani says her role in the Plant-A-Tree Programme is now that of a "multiplier". Over the years, she has been preaching about the importance of planting trees.
Mrs Mekani said that one of her earliest connections with nature was when she came across a compost pit at a factory in India.
"I said, 'Yuck, such a dirty smelly pit' and so my dad had called the gardener and said that maybe I should spend time with him tomorrow," she told The Straits Times.
The gardener took her to a pit where composting had been completed and she played with the soil. "And then cheekily, that caretaker took me to that first pit, which was (smelly), and says, 'This, after three to four months, becomes like that.'
"Now that was my eureka moment. It just kind of struck me, nature's way of recycling," she said.
She believes in the need for young people to be in contact with nature as they are living in such a "virtual world".
To that end, Mrs Mekani has reached out to many schools to encourage them to participate in the Plant-A-Tree Programme. One of them is Wellington Primary School. Principal Gary Tsu said: " We believe that the environmental conservation efforts cannot be complete without the 'learning by doing' or hands-on educational effort."
Her donations have also helped to build tree nurseries in the two campuses of the United World College of South East Asia in Tampines and Dover.
Managed by students, the nurseries come under the Rainforest Restoration Project, which aims to grow mainly vulnerable and critically endangered rainforest plant species.
Mrs Mekani said: "I believe that we all have our part to play in this journey of life. Perhaps loving and promoting nature in my home of Singapore is my calling.
"Along the way, if my efforts, however small, have inspired others to actively pursue their passions, making our community a better place - then my life will have been well lived."