An idol of Ganesh immerged from mandar tree or especially made up from the wood of mandar tree is called as Mandar Ganesh.
If someone worships mandar tree continuously for twenty one years with watering the mandar tree and offering gandha(sandalwood paste), red lead and flowers on the roots of the tree then one can see the shape of Ganesh. (Ganesh is immerged from the root of the mandar tree) This is one type of Mandar Ganesh. Second type of Mandar Ganesh, is when someone worships mandar tree for some time and then from the wood of mandar tree he carves an idol.
How to get first type of mandar Ganesh ?
One can experience the immerging of mandar ganesh by worshipping white mandar tree (the colour of the flowers is white some mandar trees have blueish white, whitish purple flowers) for twenty one years with dhoop, deep/light, naivedya (offering to God), offering durva and with pradakshirna (circumambulation). After twenty one years the shape of Lord Ganesha is immerged at the root of the tree.
How to get second type of mandar Ganesh?
Worship Ganesh on Angarika Chaturthi (Krishna Chaturthi which comes on Tuesday) or for continuous 21 days under the mandar tree and then cut the portion of the tree religiously and make the idol from it.
The beads made form Mandar tree have a very significant meaning in worhipping of Lord Ganesh. It is believed that Lord Ganesha stays in the roots of mandar tree on magh shuddha saptami (rathsaptami). It is believed that if one does penance of Lord Ganesha under a mandar tree, his (or hers) wishes are bound to come true.
An examples of mandar ganesh (second type)
Puja of an idol of Mandar (Ganesh second type)
Wipe it with a clean washed piece of cloth(for the idol is of wood).
Put tikka, a round circle of wet sandalwood paste .
Then sprinkle haldi and kunku.
Then apply on the tikka ,a dry dry coat of ashtagandha and shendur(red lead).
Then offer flowers, durvas and shami.
Offer Deep. A small metal lamp with two wicks (a bud shaped cotton dipped in oil and cotton is lit). Which one can move in clockwise direction before God and placed in front of the God.
Offering Naivedya - dip two finger tips of right hand(the index and the middle fingers) in water and do a mandal on ground or flat surface.(mandal is a square shape figure made by water with two fingers).
Offer pastil stick.
Place an offering for it. Take water in the fingertips and move it around the offering in clockwise direction for three times. Simultaneously close the eyes with touching left hand's thumb & index finger.